JP6932986B2 - Fixing device and image forming device - Google Patents

Description

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

Conventionally, an electrostatic latent image formed on a photoconductor is developed with toner to form a toner image, the formed toner image is transferred to paper, and the transferred toner image is transferred to a heated fixing roller in a fixing device. An electrophotographic image forming apparatus is used in which a nip portion formed of a toner and a pressurizing roller is passed through a paper to heat and fix the toner to form an image on the paper.

In such an image forming apparatus, the curvature separability of the paper is ensured by forming the nip portion in the fixing apparatus into a convex shape. That is, since the fixing belt stretched on the fixing roller has a curvature at the outlet of the nip portion, the paper is peeled off from the curved fixing belt due to its own rigidity.

However, when passing envelope-shaped paper, the convex shape of the nip portion causes a difference in transport distance between the paper on the upper surface and the paper on the lower surface, causing wrinkles, image misalignment, and the like. There are two ways to solve such problems.
The first is a fixing device having a flat nip shape in which the hardness of the fixing roller and the pressure roller are the same and the shape of the nip portion is flat. However, if the flat nip shape is used, there is no problem in the separability of high-rigidity paper such as thick paper and envelopes, but the separability of low-rigidity paper such as plain paper cannot be ensured, and the paper after passing through the nip portion is fixed. Paper jams occur when the paper is not peeled off from the belt. Therefore, such a fixing device is dedicated to envelopes.

On the other hand, as a second method, Patent Document 1 discloses a technique of reducing the nip load when passing an envelope to bring it closer to a flat nip shape. That is, when passing plain paper, the nip portion is made convex by increasing the nip load, and the curvature separability of the paper is ensured. At this time, the separation pad is arranged inside the fixing belt and on the downstream side of the nip portion, and the fixing belt is pressed against the pressure roller side to further improve the separability in the nip portion.
On the other hand, when passing an envelope with high separability, wrinkles and image misalignment are suppressed by forming the nip portion into a flat nip shape. At this time, in order to align the positional relationship between the separation pad and the outlet of the nip before lowering the load, the separation pad is controlled to be brought closer to the outlet of the nip.

JP-A-2015-69041

However, in the fixing device described in Patent Document 1, by reducing the load of the nip portion, the nip width becomes small, and sufficient fixing property cannot be ensured. Further, by bringing the separation pad closer to the vicinity of the outlet of the nip portion when passing the envelope, the fixing belt near the outlet of the nip portion is given a curvature, resulting in wrinkles and image misalignment.

The present invention has been made in view of the above problems, and is a fixing device and an image forming device capable of reducing wrinkles and image misalignment when passing an envelope while ensuring fixability and separability when passing plain paper. The purpose is to provide.

In order to solve the above problem, the fixing device according to claim 1 is used.
With an endless fixing belt,
A heating member that heats the fixing belt and
The first pressurizing member arranged inside the fixing belt and
Through the fixing belt heated by the heating member, the paper is pressed against the first pressure member to fix the toner image formed on the paper, and the second pressure member.
A curvature imparting member arranged inside the fixing belt and downstream of the paper transport direction of the nip portion formed between the first pressure member and the second pressure member.
The curvature imparting member was moved away from the nip portion at the first position where the region on the downstream side of the nip portion of the fixing belt was pressed toward the second pressure member side and bent, and at the first position. A second position, which is a position, a movement mechanism that makes it movable to, and
A control unit that controls the movement of the curvature imparting member is provided.
The moving mechanism includes a tension changing member that changes the tension of the fixing belt.
The control unit
By changing the tension of the fixing belt by the tension changing member, the curvature imparting member is moved.
When the envelope-shaped paper is passed through the paper, the curvature-imparting member is moved to the second position by the moving mechanism.

The invention according to claim 2 is the fixing device according to claim 1.
The moving mechanism is arranged inside the fixing belt and includes a tensioning member for tensioning the fixing belt.
The tension changing member is characterized in that the tension of the fixing belt is changed by moving the tensioning member.

The invention according to claim 3 is the fixing device according to claim 1 or 2.
The control unit is characterized in that the curvature imparting member is moved from the first position to the second position by increasing the tension of the fixing belt by the tension changing member.

The invention according to claim 4 is the fixing device according to any one of claims 1 to 3.
The nip portion is characterized in that it is substantially flat.

The invention according to claim 5 is the fixing device according to claim 4.
The first pressure member and the second pressure member have substantially the same hardness.

The invention according to claim 6 is the fixing device according to any one of claims 1 to 5.
The curvature imparting member is characterized by being a separation pad made of a single rigid body provided over the entire width direction of the fixing belt.

The image forming apparatus according to claim 7 is
An image forming part that forms a toner image on paper,
The fixing device according to any one of claims 1 to 6 is provided, wherein the paper is heat-pressed to fix the toner image on the paper.

According to the present invention, it is possible to provide a fixing device and an image forming device capable of reducing wrinkles and image misalignment when passing envelope paper while ensuring fixability and separability when passing plain paper.

It is a figure which shows the schematic structure of the image forming apparatus which concerns on embodiment to which this invention is applied. It is a block diagram which shows the main functional structure of the image forming apparatus which concerns on embodiment to which this invention is applied. It is a figure which shows an example of the schematic structure of the image fixing part which concerns on embodiment to which this invention is applied. It is a figure which shows an example of the calculation method of a nip shape. It is a figure which shows an example of the schematic structure of the image fixing part which concerns on embodiment to which this invention is applied. It is a figure which shows the modification of the curvature imparting member. It is a figure which shows the modification of the image fixing part.

Hereinafter, embodiments of the image forming apparatus of the present invention will be described with reference to the drawings. In the embodiment of the present invention, a color image forming apparatus will be described as an example, but the present invention is not limited to this, and can be applied to, for example, a monochrome image forming apparatus.

[Configuration of image forming apparatus]
FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 1 according to the present embodiment. FIG. 2 is a block diagram showing a main functional configuration of the image forming apparatus 1.

The image forming apparatus 1 includes a control unit 10, a storage unit 11, an operation unit 12, a display unit 13, an interface 14, and a control unit 10 having a CPU (Central Processing Unit) 101, a RAM (Random Access Memory) 102, and a ROM (Read Only Memory) 103. It includes a scanner 15, an image processing unit 16, an image forming unit 17, an image fixing unit 18, a transport unit 20, and the like. The control unit 10 is connected to the storage unit 11, the operation unit 12, the display unit 13, the interface 14, the scanner 15, the image processing unit 16, the image forming unit 17, the image fixing unit 18, and the transport unit 20 via the bus 21. There is.

The CPU 101 reads and executes a control program stored in the ROM 103 or the storage unit 11 to perform various arithmetic processes.

The RAM 102 provides the CPU 101 with a working memory space and stores temporary data.

The ROM 103 stores various control programs, setting data, and the like executed by the CPU 101. Instead of the ROM 103, a rewritable non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory may be used.

The control unit 10 including the CPU 101, RAM 102, and ROM 103 controls each unit of the image forming apparatus 1 in accordance with the above-mentioned various control programs. For example, the control unit 10 causes the image processing unit 16 to perform predetermined image processing on the image data and stores the image data in the storage unit 11. Further, the control unit 10 conveys the paper to the conveying unit 20, and causes the image forming unit 17 to form an image on the paper based on the image data stored in the storage unit 11.

The storage unit 11 is configured by a storage means such as a DRAM (Dynamic Random Access Memory) or an HDD (Hard Disk Drive), which is a semiconductor memory, and is input from the outside via the image data acquired by the scanner 15 or the interface 14. Image data and the like are stored. Note that these image data and the like may be stored in the RAM 102.

The operation unit 12 includes input devices such as a touch panel arranged so as to be superimposed on the operation keys and the screen of the display unit 13, and converts input operations for these input devices into operation signals and outputs them to the control unit 10.

The display unit 13 includes a display device such as an LCD (Liquid crystal display), and displays an operation screen or the like showing the state of the image forming device 1 or the content of an input operation on the touch panel.

The interface 14 is a means for transmitting and receiving data to and from an external computer, another image forming apparatus, and the like, and is composed of, for example, any of various serial interfaces.

The scanner 15 reads the image formed on the paper, generates image data including monochromatic image data for each of the color components of R (red), G (green), and B (blue), and stores the image data in the storage unit 11.

The image processing unit 16 includes, for example, a rasterization processing unit, a color conversion unit, a gradation correction unit, and a halftone processing unit, and performs various image processing on the image data stored in the storage unit 11 and stores the image data in the storage unit 11. ..

The image forming unit 17 forms an image on paper based on the image data stored in the storage unit 11. The image forming unit 17 includes four sets of exposure units 171, a photoconductor drum 172, and a developing unit 173 corresponding to the color components of C (cyan), M (magenta), Y (yellow), and K (black), respectively. There is. Further, the image forming unit 17 includes a transfer body 174 and a secondary transfer roller 175.

The exposure unit 171 includes an LD (Laser Diode) as a light emitting element. The exposure unit 171 drives the LD based on the image data, irradiates the charged photoconductor drum 172 with laser light, and exposes the photoconductor drum 172 to form an electrostatic latent image on the photoconductor drum 172. The developing unit 173 supplies toner (coloring material) of a predetermined color (any of C, M, Y, and K) by a developing roller charged on the exposed photoconductor drum 172, and is placed on the photoconductor drum 172. The electrostatic latent image formed in is developed.
An image (monochromatic image) formed of C, M, Y, and K toners on each of the four photoconductor drums 172 corresponding to C, M, Y, and K is formed from each photoconductor drum 172 onto the transfer body 174. They are sequentially stacked and transferred. As a result, a color image having C, M, Y and K as color components is formed on the transfer body 174. The transfer body 174 is an endless belt wound around a plurality of transfer body transfer rollers, and rotates according to the rotation of each transfer body transfer roller.
The secondary transfer roller 175 transfers the color image on the transfer body 174 onto the paper fed from the paper feed tray 22 or the paper feed device provided outside. Specifically, the transfer body 174 is formed by sandwiching the paper and the transfer body 174 in the transfer nip portion formed by pressure contacting the pair of secondary transfer rollers 175 and applying a predetermined transfer voltage to the secondary transfer roller 175. The toner forming the color image above is attracted to the paper side and transferred to the paper.

The image fixing unit 18 heats and pressurizes the paper on which the toner is transferred to fix the toner on the paper.
FIG. 3 is a schematic view showing the configuration of the image fixing unit 18. The image fixing portion 18 is provided via a fixing roller 181 (first pressurizing member), a heating roller 182 (tension member), a fixing roller 181 and a fixing belt 183 stretched on the heating roller 182, and a fixing roller 183. The pressure roller 184 (second pressure member) crimped to 181 is arranged inside the heating roller 182, and is arranged inside the halogen lamp heater 182a (heating member) extending in the direction of the rotation axis and the fixing belt 183. The separation pad 191 (curvature imparting member), the elongated hole 192 that supports the axial end portion of the separation pad 191, and the moving mechanism 193 that moves the separation pad 191 along the elongated hole 192 are provided. The image fixing unit 18 and the control unit 10 constitute a fixing device.
Here, the left-right direction is the X direction with respect to the paper surface of FIG. 3, and the vertical direction is the Y direction with respect to the paper surface.

The fixing belt 183 is stretched on the fixing roller 181 and the heating roller 182, and the fixing roller 181 and the pressure roller 184 provide a nip portion as a pressure contact portion for sandwiching and transporting the paper via the fixing belt 183. Constitute.
The fixing belt 183 has a structure in which an elastic layer made of silicone rubber and a surface release layer made of a fluororesin are sequentially laminated on the outer peripheral surface of a film base material made of, for example, heat-resistant polyimide. The fluororesin contains, or preferably mainly comprises any of PFA (perfluoroalkoxy alkane), PTFE (polytetrafluoroethylene), and FEP (fluorinated ethylene / propylene hexafluorinated copolymer). Will be done. As a result, the surface releasability of the fixing belt 183 with respect to the wax contained in the toner resin and the toner particles is improved, and the toner can be prevented from adhering to the fixing belt 183 at the time of fixing.

The heating roller 182 has a structure in which a resin layer made of PFTE or the like is formed on the outer peripheral surface of a core metal synthesized from aluminum or the like. Inside the core metal, a halogen lamp heater 182a and a shaft 182b extending in the direction of the rotation axis are provided. The halogen lamp heater 182a generates heat when energized under the control of the control unit 10, and heats the fixing belt 183 via the core metal and the resin layer.
The fixing belt 183 may be heated by electromagnetic induction heating (IH) without using the heating roller 182. In this case, the substrate of the fixing belt 183 is made of a material capable of electromagnetic induction heat generation such as Ni.
Further, the heating roller 182 functions as a tensioning member that stretches the fixing belt 183 together with the fixing roller 181 and applies tension to the fixing belt 183. The support shaft of the heating roller 182 is provided so as to be movable in the Y direction, and the movement is controlled by the moving mechanism 193 as described later.

As the first pressurizing member, the fixing roller 181 is crimped to the pressurizing roller 184 via the fixing belt 83, and is driven to rotate with the rotation of the pressurizing roller 184. It should be noted that, instead of the pressure roller 184, the heating roller 182 interlocked by the tension of the fixing belt 183 is driven and rotated by a rotation driving means such as a motor (not shown) under the control of the control unit 10, and the fixing roller 181 is rotated. It may be a driven rotation along with the above.
The fixing roller 181 has a structure in which an elastic layer made of silicone rubber or the like is formed on the outer peripheral surface of a columnar core metal made of iron or the like. Further, it is also possible to form a surface release layer made of a fluororesin as described above on the outer peripheral surface of the elastic layer.

As shown in FIG. 3A, the pressure roller 184 is urged in a direction approaching the fixing roller 181 by an elastic member or the like (not shown), and is pressed against the fixing roller 181 via the fixing belt 183 as a second pressure member. Then, while forming a nip portion NP with the fixing roller 181, the nip portion NP is driven by a rotation driving means such as a motor (not shown) under the control of the control unit 10 to rotate. The pressurizing roller 184 may be driven to rotate with the rotation of the fixing roller 181, or a heating source such as a halogen lamp heater may be built in the pressurizing roller 184.

The structure of the pressure roller 184 is the same as that of the fixing roller 181, and the hardness of the elastic layer of the fixing roller 181 and the elastic layer of the pressure roller 184 are substantially the same. Therefore, the nip portion NP between the fixing roller 181 and the pressure roller 184 has a substantially flat nip shape that is substantially flat in the paper transport direction.

The fixing roller 181 and the pressure roller 184 sandwich the paper between the nip portions NP, heat and pressurize the paper while transporting the paper in a predetermined transport direction, and melt and fix the toner on the paper. The halogen lamp heater 182a heats the heating roller 182 via the heating roller 182 so that the temperature of the fixing belt 183 is, for example, in the range of 180 ° C. or higher and 200 ° C. or lower.

The separation pad 191 is arranged inside the fixing belt 183 and on the downstream side of the nip portion NP. The axial end of the separation pad 191 is supported by an elongated hole 192 formed on the wall surface of the housing of the fixing device so as to extend in the Y direction, and is provided so as to be movable in the Y direction along the elongated hole 192. Has been done.

As shown in FIG. 3, the moving mechanism 193 includes a support plate 193b arranged so as to come into contact with the lower surface of a shaft 182b arranged inside the heating roller 182, one end of which is in the housing of the fixing device, and the other end of which. A spring 193a connected to the support plate 193b and urging the heating roller 182 upward, an elliptical cam 193c abutting on the lower surface of the support plate 193b, and a drive unit 193d for rotationally driving the cam 193c (see FIG. 2). ), And the tension of the fixing belt 183 is changed, and the separation pad 191 is moved along the elongated hole 192.

As shown in FIG. 3A, when the distance between the contact point between the support plate 193b and the cam 193c in contact with the support plate 193b and the axis of the cam 193c is minimized due to the rotation of the cam 193c, the support plate 193b is released. The shaft 182b, which moves downward and is supported by the support plate 193b, moves downward accordingly, so that the heating roller 182 is lowered and the tension of the fixing belt 183 is reduced.
Further, as shown in FIG. 3B, when the distance between the contact point between the support plate 193b and the cam 193c in contact with the support plate 193b and the axis of the cam 193c becomes maximum due to the rotation of the cam 193c, the support plate The 193b moves upward, and the shaft 182b supported by the support plate 193b moves upward accordingly, so that the heating roller 182 rises and the tension of the fixing belt 183 increases.
The drive unit 193d includes a solenoid, a motor, and the like, and rotationally drives the cam 193c under the control of the control unit 10.

That is, the moving mechanism 193 moves the heating roller 182 up and down by changing the distance between the contact point between the support plates 193b and 193c and the shaft of the cam 193c, and changes the tension of the fixing belt 183 accordingly.

As shown in FIG. 1, the transport unit 20 includes a plurality of paper transport rollers for transporting paper by rotating while sandwiching the paper, and transports the paper in a predetermined transport path. The transport unit 20 includes a reversing mechanism 201 that reverses the front and back sides of the paper that has been fixed by the image fixing unit 18 and transports the paper to the secondary transfer roller 175. In the image forming apparatus 1, when an image is formed on both sides of the paper, the front and back sides of the paper are inverted by the reversing mechanism 201 to form an image on both sides, and then the paper is ejected to the paper ejection tray 23. When the image is formed on only one side of the paper, the paper on which the image is formed on one side is ejected to the paper ejection tray 23 without the front and back sides of the paper being reversed by the reversing mechanism 201.

[Operation of separation pad]
Next, the operation of the separation pad 191 according to the present embodiment will be described.

The nip portion NP of the fixing device in the present embodiment has a substantially flat shape in order to suppress wrinkles and the like generated in the envelope when the envelope is passed. However, if the nip portion NP has a substantially flat shape, the paper from the fixing belt 183 or the pressure roller 184 is sufficient when passing paper having low separability such as plain paper through the substantially flat shape nip portion NP. So-called separation failure may occur.

In response to such a problem, in the present embodiment, as shown in FIG. 3A, when passing plain paper having low separability, the separation pad 191 is arranged in the region immediately after passing through the nip portion. .. That is, the separation pad 191 presses the fixing belt 183 from the inside of the fixing belt 183 toward the pressure roller 184 side as a curvature imparting member, and the shape of the fixing belt 183 near the outlet of the nip portion NP is changed to the pressure roller 184 side. The shape should be convex. As a result, even in the nip portion NP having a substantially flat nip shape, the nip portion has an upward convex nip shape (a shape that is convex toward the fixing roller 181 side) or a downward convex nip shape (a shape that is convex toward the pressure roller 184 side). It is possible to secure the same curvature separability as.

On the other hand, when the envelope is passed through the envelope, the separation pad 191 presses the fixing belt 183 near the exit of the nip portion NP to give the envelope a curvature as described above. There is a risk of causing wrinkles in the envelope and image misalignment.
Therefore, when passing the envelope, the separation pad 191 is moved to a position where the fixing belt 183 is not pressed, as shown in FIG. 3 (B). Since the envelope has higher rigidity and higher separability than plain paper, sufficient separability can be ensured without imparting curvature as described above.

Specifically, when passing plain paper, the moving mechanism 193 moves the heating roller 182 downward, as shown in FIG. 3A. At this time, the separation pad 191 moves in the Y direction along the elongated hole 192, stops at the position closest to the pressure roller 184 (the lowest position in the Y direction: the first position), and puts the fixing belt 183 inside. Presses from to the pressure roller 184 side. As a result, the paper that has passed through the nip portion formed between the fixing roller 181 and the pressure roller 184 can be imparted with curvature separability from the fixing belt 183.

On the other hand, when the envelope is passed through, as shown in FIG. 3B, the moving mechanism 193 moves the heating roller 182 upward to apply tension to the fixing belt 183. As a result, the separation pad 191 moves in the Y direction along the elongated hole 192 and stops at the position farthest from the pressure roller 184 (the highest position in the Y direction: the second position), so that the fixing belt 183 Is not pressed, and the curvature separability is not imparted.

[Fixation separation experiment]
Hereinafter, an experiment for verifying the relationship between the shape of the nip portion NP and the fixing separability will be described.

(Evaluation method)
(1) Evaluation of Paper Misalignment Amount of misalignment of two sheets in the paper transport direction was measured by stacking two thick papers while shaking the shape of the nip portion NP. The evaluation result was that the deviation amount was 1.0 [mm] or less, which was good. The thickness of the thick paper is 300 μm, and the size is A3.
(2) Evaluation of image misalignment and wrinkles An envelope was passed through the nip part NP similar to (1), and image misalignment and wrinkles were confirmed.

(Flat nip shape)
The shape of the nip portion NP capable of maximizing the effect of the present embodiment is a flat nip shape having a completely flat shape in the paper transport direction. The flat nip shape is realized when the hardness and thickness of the fixing roller 181 and the pressure roller 184 are the same.
Therefore, a flat nip shape is formed by the following fixing device, and the fixing separability is verified.
1. 1. Fixing roller 181
A fixing roller 181 having an outer diameter of φ60 mm, a core metal diameter of φ40 mm, and an elastic layer having a thickness of 10 mm was used. The elastic layer is made of silicone rubber with ASKER C hardness of 30 °. The fixing roller 181 rotates drivenly with the rotation of the pressure roller 184 while forming a nip portion between the fixing roller 181 and the pressure roller 184.
2. Fixing belt 183
A fixing belt 183 having an outer diameter of φ99 mm was used. It is based on a polyimide having a thickness of 70 μm, and has an elastic layer made of silicone rubber having a thickness of 200 μm and a surface layer made of PFA.
3. 3. Pressurized roller 184
A pressure roller 184 having an outer diameter of φ60 mm, a core metal diameter of φ40 mm, and an elastic layer having a thickness of 10 mm was used. The elastic layer is made of silicone rubber having an ASKERC hardness of 30 °, and has a surface layer made of PFA coating on its surface. Under the control of the control unit 10, it is driven by a rotation driving means such as a motor to rotate.
4. Fixing load The fixing load applied to the nip portion NP was set to 1000N.
5. Belt tension The tension on each of the upstream side and downstream side of the fixing belt 183 in the paper transport direction was set to 20N with the fixing roller 181 sandwiched therein, and a total of 40N was used as the belt tension.

(Approximately flat nip shape)
In a fixing device having a substantially flat nip shape that is close to the flat nip shape and has a slight curvature, the fixing separability is verified.
A method of calculating the shape of the nip portion NP will be described. The shape of the nip portion NP is changed by changing the hardness and thickness of the fixing roller 181 and the pressure roller 184.

FIG. 4 is a diagram illustrating how to obtain the nip shape.
Assuming that the radius of curvature of the fixing roller 181 is R, the nip portion NP has a flat nip shape at R = ∞. Assuming that the center angle of the nip portion NP is θ and the nip width is l, l is obtained by the following equation (1).
l = Rθ ・ ・ ・ (1)

Let the radius of curvature of the center line of the lower paper S1 and the arc length within the nip width be R1 and l1, respectively. Further, the radius of curvature of the center line of the upper paper S2 and the arc length within the nip width are R2 and l2, respectively. Further, the thickness of the thick paper is T (T = R2-R1). The difference in arc length within the nip width between the lower paper S1 and the upper paper S2 can be obtained as the following formula (2) by using the above formula (1).
l2-l1 = R2θ-R1θ
= (R2-R1) θ
= Tθ ・ ・ ・ (2)

Further, assuming that the difference in arc length per unit length is Δl, Δl can be obtained by the following equation (3).
Δl = (l2-l1) / l ... (3)

Assuming that the length of the paper in the transport direction is L, the amount of deviation ΔL between the rear ends of the lower paper S1 and the upper paper S2 can be obtained as follows using the above equations (1) to (3).
ΔL = Δl * L
= (L2-l1) / l * L
= Tθ / l * L
= T / R * L ... (4)

Here, the amount of deviation ΔL at the rear end when two thick papers of T = 0.3 [mm] and L = 420 [mm] are passed in layers is as follows using the above formula (4). Is required.
ΔL = 0.3 / R * 420
= 126 / R

That is, it can be seen that the radius of curvature should be R ≧ 126 in order to reduce the amount of deviation ΔL at the rear end to 1 mm or less. Therefore, in this experiment, the shape of the nip portion NP such that R ≧ 126 is a substantially flat nip shape.

(result)
The above evaluation was performed while shaking the shape of the nip portion by making the fixing roller and the pressure roller different.
The results of this experiment are shown in Table 1. The radius of curvature R is obtained by performing simulation analysis of the nip shape at each roller configuration and calculating the radius of curvature R at that time.

(1) Evaluation of Paper Misalignment As shown in Table I, the misalignment of the rear edge of the paper was 1 [mm] or less when R ≧ 120. As described above, it is desirable that the radius of curvature R is R ≧ 126 in the calculation, but it can be seen in the experiment that the amount of deviation of the rear end of the paper is an appropriate value at a value close to this.
(2) Evaluation of image misalignment and wrinkles It was clarified that wrinkles and image misalignment that occur when the envelope is passed through are also suppressed when R ≧ 120.

As described above, from this experiment, it is clear that the effect of the present invention can be sufficiently exhibited when the nip portion NP has a flat nip shape or a substantially flat nip shape.

As described above, the fixing device according to the present embodiment includes a separation pad 191 as a curvature imparting member arranged inside the fixing belt 183. The separation pad 191 is arranged at the first position where the vicinity of the outlet of the nip portion NP is pressed and bent when passing plain paper, and the second separation pad 191 is moved away from the nip portion NP when passing the envelope. Move to the position of. Therefore, when passing plain paper, the curvature of the fixing belt 183 ensures sufficient separability, and when passing two sheets of paper, the difference in transport speed between the upper and lower papers is suppressed, and envelope wrinkles and image misalignment are suppressed. Etc. can be prevented.

Further, the fixing device according to the present embodiment includes a moving mechanism 193, changes the belt tension of the fixing belt 183 under the control of the control unit 10, and moves the separation pad 191 accordingly. Therefore, since a mechanism for moving the separation pad itself is not required, it can be realized without significantly affecting the configuration in the vicinity of the nip portion NP.

Further, the fixing device according to the present embodiment changes the belt tension of the fixing belt 183 by moving the heating roller 182 as the tensioning member by the moving mechanism 193. Therefore, the belt tension can be changed with a relatively simple configuration, which can be realized at low cost.

Further, the fixing device according to the present embodiment moves the separation pad 191 to the first position by increasing the belt tension of the fixing belt 183 by the moving mechanism 193. Therefore, since the envelope can be passed while maintaining the belt tension higher than that when the plain paper is passed, there is no possibility that the fixing belt 183 may be loosened, resulting in poor fixing.

Further, in the fixing device according to the present embodiment, the nip portion NP has a flat nip shape or a substantially flat nip shape. Therefore, as compared with the case where the nip portion NP has an upward convex nip shape or a downward convex nip shape, there is no possibility that envelope wrinkles or image misalignment occur when passing through the nip portion NP. Further, as described above, since the effect of the present invention can be obtained even in a substantially flat nip shape, the range in which the fixing roller 181 and the pressure roller 184 can be combined is wide.

Further, in the fixing device according to the present embodiment, a flat nip shape can be formed by making the hardness and the thickness of the fixing roller 181 and the pressure roller 184 the same. As described above, the flat nip shape can provide the highest effect.

Further, the fixing device according to the present embodiment is a separation pad 191 made of one rigid body provided as a curvature imparting member over the entire width direction of the fixing belt 183. Therefore, the curvature imparting member can be constructed by a relatively inexpensive member.

[Other Embodiments]
Although the above embodiment has been specifically described based on the embodiment of the present invention, the above embodiment is a preferable example of the present invention and is not limited thereto.

In the above embodiment, a method of controlling the separation pad 191 so as to move away from the nip portion NP by increasing the belt tension of the fixing belt 183 when the envelope is passed has been described, but the present invention is not limited to this.
For example, by arranging the elongated holes 192 so as to extend long in the X direction as shown in FIG. 5, the separation pad 191 is kept away from the nip portion NP by lowering the belt tension of the fixing belt 183 when passing the envelope. It is possible.
That is, when passing plain paper, the separation pad 191 moves in the X direction as shown in FIG. 5 (A) and is closest to the nip portion NP (the most upstream position with respect to the paper transport direction: It is placed in the first position). On the other hand, when the envelope is passed through the envelope, the belt tension is lowered so that the separation pad 191 moves in the X direction and is away from the nip portion NP (most relative to the paper transport direction) as shown in FIG. 5 (B). Since it moves to the downstream position (second position), the curvature near the exit of the nip portion NP can be reduced.

Further, in the above embodiment, the separation pad 191 is moved according to the change in the belt tension of the fixing belt 183, but the present invention is not limited to this. For example, a support member that supports the axial end of the fixing roller 181 of the separation pad 191, a cam mechanism that contacts the support member, and a motor that applies a driving force to the cam mechanism are provided, and are controlled by the control unit 10. The motor may be driven by the above, and the separation pad 191 may be moved by the operation of the cam mechanism.

Further, in the above embodiment, the separation pad 191 is used as the curvature imparting member, but the present invention is not limited to this.
FIG. 6 shows a modified example of the curvature imparting member. As shown in FIG. 6A, it is also possible to use a roller or a roller 191a as the curvature imparting member. The axial end of the roller or roller 191a can be movably provided along an elongated hole (not shown) formed in the housing of the fixing device.
Further, as shown in FIG. 6B, it is also possible to use a belt 191b stretched on two rollers as a curvature imparting member. Axial ends of the two rollers can be movably provided along elongated holes (not shown) formed in the housing of the fixing device.

Further, in the above embodiment, a so-called biaxial tension fixing belt having a fixing roller 181 and a heating roller 182 inside the fixing belt 183 is used, but the present invention is not limited to this.
The present invention can also be applied to a fixing device using a pressure pad 185 as a first pressure member and a halogen lamp heater 182a as a heating means as shown in FIG. 7 (A). In this case, since the heating roller 182 for tensioning the fixing belt is not provided inside the fixing belt 183, the fixing belt 183 is tensioned by the tensioning member 186 that can move in the Y direction. The moving mechanism 193 is composed of the spring 193a, the support plate 193b, and the driving unit 193d as in the above embodiment, and the arrangement of the separation pad 191 is changed by moving the tension member 186 in the Y direction as shown in the figure. do.
Further, as shown in FIG. 7B, in addition to the fixing roller 181 and the heating roller 182, the fixing device provided with the tension roller 187 for tensioning the fixing belt 183 inside the fixing belt 183. The present invention is applicable. In this case, as in the above embodiment, the moving mechanism 193 is configured by the spring 193a, the support plate 193b, and the driving unit 193d, and the heating roller 182 can be moved as shown in the figure. Alternatively, the tension roller 187 may be provided so as to be movable in the Y direction, and the tension roller 187 may be moved by the moving mechanism 193 to change the belt tension.

In addition, the detailed configuration of each device constituting the image forming apparatus and the detailed operation of each device can be appropriately changed without departing from the gist of the present invention.

1 Image forming device 10 Control unit 18 Image fixing unit 181 Fixing roller (first pressurizing member)
182 Heating roller (tension member)
182a Halogen lamp heater (heating member)
183 Fixing belt 184 Pressurizing roller (second pressurizing member)
185 Pressurizing pad (first pressurizing member)
186 Tension member 187 Tension roller (tension member)
191 Separation pad (curvature imparting member)
192 Long hole 193 Moving mechanism 193a Spring (tension changing member)
193b Support plate (tension changing member)
193c cam (tension changing member)
193d Drive unit (tension changing member)

Claims (7)

With an endless fixing belt,
A heating member that heats the fixing belt and
The first pressurizing member arranged inside the fixing belt and
Through the fixing belt heated by the heating member, the paper is pressed against the first pressure member to fix the toner image formed on the paper, and the second pressure member.
A curvature imparting member arranged inside the fixing belt and downstream of the paper transport direction of the nip portion formed between the first pressure member and the second pressure member.
The curvature imparting member was moved away from the nip portion at the first position where the region on the downstream side of the nip portion of the fixing belt was pressed toward the second pressure member side and bent, and at the first position. A second position, which is a position, a movement mechanism that makes it movable to, and
A control unit that controls the movement of the curvature imparting member is provided.
The moving mechanism includes a tension changing member that changes the tension of the fixing belt.
The control unit
By changing the tension of the fixing belt by the tension changing member, the curvature imparting member is moved.
A fixing device characterized in that the curvature imparting member is moved to the second position by the moving mechanism when passing envelope-shaped paper. The moving mechanism is arranged inside the fixing belt and includes a tensioning member for tensioning the fixing belt.
The fixing device according to claim 1 , wherein the tension changing member changes the tension of the fixing belt by moving the tension member. Claim 1 or 2 characterized in that the control unit moves the curvature imparting member from the first position to the second position by increasing the tension of the fixing belt by the tension changing member. The fixing device according to. The fixing device according to any one of claims 1 to 3 , wherein the nip portion is substantially flat. The fixing device according to claim 4 , wherein the hardness of the first pressure member and the second pressure member are substantially the same. The fixing according to any one of claims 1 to 5 , wherein the curvature imparting member is a separation pad made of a single rigid body provided over the entire width direction of the fixing belt. Device. An image forming part that forms a toner image on paper,
An image forming apparatus comprising the fixing device according to any one of claims 1 to 6 , wherein the paper is heat-pressed to fix the toner image on the paper.

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