JPH11224011A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of fixing unfixed toner carried on a record medium without disturbing the unfixed toner, now matter how much the recording medium in transfer is curved (curled), and also, for suppressing the offset of the record medium after finishing a fixing operation. SOLUTION: The fixing device 10 is provided with a fixing roll 28, and a pressure roll 30 which is energized so as to come into contact with the fixing roll 28 with rotation, and by making the sheet with the unfixed toner carried on its surface pass through the nip part of the fixing roll 28 and the pressure roll 30 in one-way direction, the unfixed toner is fixed on to the sheet. In this case, the device is provided with a heating roll 34 arranged nearly above the fixing roll 28 and adjacent to the roll 28, and with a heat generating source 32 inside, and a heat transmission belt 36 which is laid to be stretched between the heating roll 34 and the fixing roll 28 in an endless state, and for heating the unfixed toner on the sheet passing through the nip part in accordance with the heat transmission from the heat generating source 32. And, the fixing roll 28 is formed of an elastic roll with an elastic layer installed on the outer periphery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a fixing device used for melting and pressing unfixed toner on a recording medium and fixing the toner on the recording medium.

[0002]

2. Description of the Related Art Conventionally, in a fixing device for an electronic image forming apparatus, instead of a conventional heating roll fixing method, for example, as shown in FIG. A fixing belt B is stretched between R1 and a heating roll R3, and a recording medium D is preheated by a belt fixing method in which a pressure roll R2 that presses the fixing roll R1 from below through the fixing belt B is provided. Technologies that combine these have been developed.

[0003] By preheating the recording medium D, the temperature of the nip portion between the pressure roll R2 and the fixing belt B can be set low, and by using the fixing belt B having a small heat capacity, the recording medium D can be used. At the time of passing through the nip portion, the temperature of the fixing belt B can be rapidly cooled. Further, this cooling causes the fixing belt B at the exit of the nip portion to move.
The cohesive force of the toner to be separated from the toner can be increased. Due to the increase of the cohesive force, the releasability of the toner from the fixing belt B and the toner can be enhanced, so that even if no oil is applied or only a small amount of oil is applied, there is no clear and clear. Thus, a stable fixed image can be obtained. As described above, the belt fixing system provides a fixing device in which the problems of both the releasability and the oil application, which cannot be solved by the conventional heating roll system, are solved at once.

[0005] Here, the structure of a conventional belt-fixing type fixing device shown in FIG. 5 will be schematically described. The fixing device includes a fixing roll R1, a pressure roll R2, and a heating and tension roll R3. A fixing belt B is stretched between R1 and the heating and tension roll R3. An oil application roll R4 is disposed above the fixing belt B, and a guide plate G is disposed below the fixing belt B with a gap. A preheating passage for the recording medium D is defined from the space between the lower portion of the fixing belt B and the guide plate G.

On the other hand, a heating source H is provided inside the heating and tension roll R3, and a heating source may be additionally provided inside the fixing roll R1 and the pressure roll R2. In order to control the temperature of the fixing belt B, a thermistor S is provided in contact with the non-sheet passing portion of the fixing belt B.

[0006]

However, in the conventional fixing device having the above-described structure, the space between the fixing belt B and the guide plate G is defined as the preheating passage for the recording medium D as described above. Therefore, when the recording medium D carrying the unfixed toner image on the upper surface is conveyed over the guide plate G, for example, the paper has a curl habit or the recording medium D is being conveyed during the conveyance. If the recording medium D is jumped up or sagged due to a difference in conveyance speed from the transfer unit, the recording medium D is lifted in a partially curved state, and the lifted portion touches the fixing belt B from below. It has been pointed out that the unfixed toner image carried here may be disturbed to cause image defects, and improvement is demanded.

On the other hand, since the above-mentioned problem is based on the existence of the fixing belt B, it is conceivable to return the fixing device to a fixing device having a conventional configuration without using the fixing belt B. In this case, the heating source H must be disposed on the fixing roll R1, and the outer peripheral surface of the fixing roll R1 must be quickly heated. As a result, if the nip width at the rolling contact portion between the fixing roll R1 and the pressure roll R2 is to be sufficiently set, the pressure roll R2 must necessarily be formed of an elastic roll.

When the pressure roll R2 is made of an elastic roll in this manner, the nip shape at the rolling contact portion is recessed downward, and the toner is carried on the upper surface of the recording medium D. In addition to the fact that the sheet easily adheres to the outer peripheral surface of the located fixing roll R1 (that is, the sheet easily offsets), the nip shape is recessed downward. It tends to adhere to the outer peripheral surface, and improvement has been demanded from the viewpoint of preventing this offset.

The present invention has been made in view of the above-described circumstances, and a main object of the present invention is to provide a recording medium which is being conveyed in any curved posture (curled state).
An object of the present invention is to provide a fixing device capable of fixing unfixed toner carried thereon without disturbing the toner.

It is another object of the present invention to provide a fixing device in which a recording medium after a fixing operation is not easily offset.

[0011]

Means for Solving the Problems The above-mentioned problems are solved,
In order to achieve the object, a fixing device according to the present invention includes a fixing roll and a pressure roll that is urged to be in rolling contact with the fixing roll. A fixing device for fixing the unfixed toner on the sheet by passing a sheet carried on the surface along a contact portion of the fixing roll and the pressure roll in one direction. A heating roll, which is disposed adjacent to the side opposite to the side on which the pressure roll is disposed and in which a heating means is disposed, and which is endlessly wound around the heating roll and the fixing roll. A heat transfer belt for receiving the heat transfer from the heat generating means and heating the unfixed toner on the sheet passing through the transfer portion, wherein the fixing roll is formed from an elastic roll having an elastic layer on the outer periphery. Been It is characterized in Rukoto.

Further, according to the second aspect of the present invention, the fixing device further includes a driving unit for driving the pressure roll to rotate, and the heat transfer belt is in frictional contact with the pressure roll. The heating roll is rotationally driven as the heat transfer belt travels.

According to a third aspect of the present invention, in the fixing device, the driving unit rotationally drives the fixing roll at a peripheral speed lower than that of the pressure roll. .

According to a fourth aspect of the present invention, in the fixing device, the fixing roll includes a driven gear mounted coaxially with the fixing roll, and the driving unit meshes with the driven gear. A driving gear is provided, and a one-way clutch is interposed between the driven gear and the fixing roll. The one-way clutch allows the fixing roller to rotate faster than the driven gear, and also includes a one-way clutch. It is characterized in that rotation slower than the driven gear is prohibited.

According to a fifth aspect of the present invention, in the fixing device according to the fifth aspect, the fixing roll includes a cored bar and an elastic member provided with a predetermined thickness on an outer periphery of the cored bar. And a layer.

According to a sixth aspect of the present invention, in the fixing device according to the sixth aspect, the pressure roll is formed of a roll having a hardness higher than a hardness of the elastic layer on the roller.

According to a seventh aspect of the present invention, the fixing device is characterized in that the pressure roll is rotatably supported around a fixed axis.

According to the fixing device of the present invention, the distance between the rotation axis of the pressure roll and the rotation axis of the fixing roll is determined by the radius of the pressure roll. It is characterized in that it is set shorter than the sum of the radii of the fixing roll.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of an embodiment of a fixing device according to the present invention will be described below in detail with reference to the accompanying drawings.

{Schematic Description of Fixing Device 10} First, as shown in FIG. 1, the fixing device 10 of this embodiment has an electronic image forming apparatus (not shown) as a housing structure, for example,
The apparatus includes a housing 12 fixed to a frame of the electronic copying apparatus. The housing 12 includes a bottom plate 14 fixed directly on the apparatus frame, side plates 16 erected from left and right side edges of the bottom plate 14, respectively. The upper cover 1 attached to the side plate 16 so as to cover a substantially upper right portion in the drawing.
8 and a left cover portion 20 attached to the side plate 16 so as to cover a substantially left portion thereof.

Here, the upper cover part 18 is fixedly attached to the side plate 16, and at the upper right part thereof,
The swing lever 22 is swingably supported so that the left side in the figure is opened around the first support shaft 24 located on the right side in the figure. On the other hand, the left cover part 20
Is swingably attached to the side plate 16 such that the upper part is opened around the support shaft 26.

Further, the fixing device 10 has a roll configuration in which a fixing roll 28 is supported by the side plate 16 so as to be rotatable around a fixed axis, and substantially below (specifically, obliquely below) the fixing roll 28. A pressure roll 30 rotatably supported by the side plate 16 around a fixed axis set in parallel with the fixing axis of the fixing roll 28 in a state of being in contact with the roller, and substantially above the fixing roll 28 (specifically, Is mounted on the swing lever 22 at a position obliquely upward, is rotatably supported around its own central axis, and includes a heating roll 34 in which a heat source 32 such as a halogen lamp is incorporated. It is configured. Further, the fixing device 10 further includes a fixing belt (heat transfer belt) 36 wound endlessly over the fixing roll 28 and the heating roll 34.

Here, although the details will be described later, the fixing roll 2
Numeral 8 is composed of an elastic roll, while pressure roll 30 is composed of a roll having a higher on-roll hardness than the elastic roll. On the other hand, the fixing roll 28 and the pressure roll 30
As shown in FIG. 2, the distance D between the centers of rotation is slightly smaller than the sum of the radius R1 of the fixing roll 28 and the radius of the pressing roll 30R2 (R1 + R2). As a result, in the rolling contact portion (nip portion) of the fixing roll 28 and the pressing roll 30, the two roll contact each other with a predetermined pressure contact force P 1, whereby the fixing roll 28 is pressed.
Is brought into a state depressed at the rolling contact portion. That is, a sufficient nip width is secured.

The fixing device 10 includes a fixing belt 3
6, a silicone oil is applied to the outer surface of the fixing belt 36, and the oil applying roll 38 for cleaning the outer surface of the fixing belt 36 is pressed against the fixing belt 36 in a state of being orthogonal thereto. 3
First coil spring 4 for applying predetermined tension to 6
0, and a second coil spring 42 that urges the heating roll 34 in a direction away from the fixing roll 28 and cooperates with the first coil spring 40 to apply a predetermined tension to the fixing belt 36. I have.

The lower right portion of the upper cover 18 in the figure is bent inward. The guide plate 44 is located below the bent piece and is largely separated therefrom. It is fixed to. From between the upper cover portion 18 and the guide plate 44, a sheet (hereinafter, simply referred to as an unfixed sheet) carrying unfixed toner on the upper surface is moved in one direction (conveying direction) indicated by an arrow in the drawing. An inlet port 46 is defined along the interior of the housing 12.

Here, the guide plate 44 is attached in such a manner as to be inclined obliquely upward and to the left in the figure so that the height thereof increases as it enters the housing 12. On the other hand, the leading end of the guide plate 44, that is, the lower right end in the figure, is located inside the electronic copying apparatus and adjacent to the entrance port 46 on the right side in the figure for sheet conveyance. The guide plate 44 is positioned so as to face the outlet end of the endless belt EB, and the leading end of the guide plate 44, that is, the upper left end in the figure, is a rolling contact portion between the fixing roll 28 and the pressure roll 30 ( Nip)
Is positioned so as to face the.

The leading end of the unfixed sheet conveyed through the endless belt EB toward the fixing device 10 in one direction (conveying direction) indicated by an arrow in FIG. , And is guided so as to be conveyed obliquely upward. As a result, the unfixed sheet guided by the guide plate 44 is guided to a rolling contact portion between the fixing roll 28 and the pressure roll 30.

On the other hand, the fixing roll 28 and the pressing roll 30
Thus, a sheet discharge path 48 for discharging a sheet on which the unfixed toner is fixed by thermocompression (hereinafter, referred to as a fixed sheet) is formed. In this embodiment, the sheet discharge path 48 The fixed sheet is set to be discharged upward in a substantially upright state.

A lower discharge roll 50 is rotatably supported by the left cover portion 20 in a state between the discharge path 48 and the rolling contact portion. The lower discharge roll 50 is described later. A configuration is adopted in which the driving force from the driving mechanism 52 is obtained and the rotation is performed at a speed equal to or higher than that of the pressure roll 30 (for example, a rotation speed set 5% faster than the speed of the pressure roll 30). Have been. The lower discharge roll 50 includes
The upper paper discharge roll 54 is in contact with the upper discharge roll 54 with a predetermined elastic force via the leaf spring 56 in a state of rolling contact from obliquely above. The position of the upper discharge roll 54 is set such that a line connecting the center positions of the upper discharge roll 54 and the lower discharge roll 50 is substantially orthogonal to the discharge path of the fixed sheet. Have been.

In the fixing device 10 having such a schematic configuration, the unfixed sheet S conveyed onto the guide plate 44 by the conveyance mechanism (not shown) is moved from the lower surface where the unfixed toner is not adhered to the guide plate 44. And is guided toward a rolling contact portion (nip portion) between the fixing roll 28 around which the fixing belt 36 is wound and the pressure roll 30.
It is set so that the toner is thermocompression-bonded and fixed on the sheet by being inserted in a state where the two 28 and 30 are pressed against each other.

{Description of Fixing Roll 28} The above-described fixing roll 28 includes a core 28A rotatably supported on a side plate 16 via a bearing (not shown), and a core 28A.
A roll body 28B is disposed coaxially around the outer periphery of A and has a fixing belt 36 wound therearound. The outer diameter of the roll is set to 38.5 mm in this embodiment. Here, in this embodiment, the core part 28A has a diameter of 25 m.
m, formed from an iron shaft, and the roll body 28B
A silicone rubber heat-resistant elastic body (specifically, Asker C) attached to the outer periphery of the cored bar 28A with a thickness of 6.75 mm.
It is formed as an elastic roll from silicone rubber sponge having a hardness of 35 degrees.

A first driven gear 58 is coaxially mounted on a shaft disposed at one end of the cored bar 28A via a one-way clutch 60, which will be described in detail later. A transmission gear 62 that constitutes a part of the drive mechanism 52, which will be described in detail later, meshes with the one driven gear 58. In this manner, the driving force from the driving mechanism 52 is transmitted to the first driven gear 58 via the transmission gear 62 as a clockwise rotational force in the drawing, and the one-way clutch 60
The rotational force is transmitted to the fixing roll 28 via the fixing roller 28.

{Description of Pressure Roll 30} The pressure roll 30 described above includes a core 30A rotatably supported on the side plate 16 via a bearing (not shown), and a core 30A.
A and a roll main body 30B coaxially arranged on the outer periphery of A, and the outer diameter of the roll is set to 35 mm.
Here, in this embodiment, the core 30A has a diameter of 3 mm.
Roll body 30B formed from a 2mm iron shaft
Is formed from a silicone rubber heat-resistant elastic body (specifically, a silicone rubber having a JIS A hardness of 20 degrees, which is harder than the above-described fixing roll 28) and is attached to the outer periphery of the cored bar 30A with a thickness of 1.5 mm. Have been. The outer periphery of the roll body 30B is covered with a 50 μm-thick fluororesin tube.

A shaft provided at one end of the cored bar 30A has a second driven gear 64 fixed coaxially thereto. The second driven gear 64 is connected to the first driven gear 64 described above. Gear 58
The driving force from this is transmitted to the second driven gear 64 via the first driven gear 58, and the pressing roll 30 moves in the counterclockwise direction opposite to the fixing roll 28. It is configured to be driven to rotate.

In this embodiment, the pressure roller 30 is set as the main drive for conveying the unfixed sheet, and the peripheral speed of the fixing roller 28 is increased even when the fixing roller 28 is thermally expanded. The gear ratio of the first and second driven gears 58 and 64 is set so that the peripheral speed of the roll 30 does not become faster. That is, the fixing roller 28 is connected to the second driven gear 6
The rotation speed at the time of rotation by 4 is set to be slightly lower than the rotation speed at the time of rotation by frictionally engaging with the pressure roll 30 via the fixing belt 36.

On the other hand, in this embodiment, the pressure roll 30 is not located immediately below the fixing roll 28, but rather in the conveying direction of the unfixed sheet rather than immediately below the fixing roll 28. It is arranged at a position deviated by
When a perpendicular line passing through the center point of the fixing roll 28 is used as a base line, a position where an angle formed by this base line and a line segment passing through both center points of the fixing roll 28 and the pressure roll 30 is a predetermined acute angle It is arranged in. In addition, this pressure roll 30
Is set so as to be substantially perpendicular to the conveying direction of the unfixed sheet.

{Description of One-Way Clutch 60} The one-way clutch 60 allows the fixing roller 28 to rotate relative to the first driven gear 58 in the clockwise direction in FIG. It is configured such that the relative rotation is locked, in other words, both rotate integrally. Specifically, in the cold state, that is, the fixing belt 36 frictionally engages with the pressure roller 30, and the fixing roller 28 frictionally engages with the fixing belt 36, and the fixing roller 28 and the fixing roller 28 are pressed by the pressure roller 30. When the fixing belt 36 is driven (rotated), the peripheral speed of the fixing roll 28 rotating clockwise in the drawing is the same as the peripheral speed of the pressure roll 30, and is lower than the peripheral speed of the first driven gear 58. This speed difference will be absorbed by the one-way clutch 60, although it will be made slightly faster.

The fixing roll 36 is heated via the fixing belt 36 by the heat generated by the heating roll 34 to be in a warm-up state, and the outer diameter of the fixing roll 36 increases due to thermal expansion, so that the peripheral speed of the fixing roll 36 increases. Even so, the speed difference is set so as not to be faster than the peripheral speed of the pressure roll 30, so even in this case, the speed difference is reliably absorbed by the one-way clutch 60.

On the other hand, such a one-way clutch 60
Is provided, the following effects are additionally achieved. That is, if such a one-way clutch 60 is not provided, when a glossy sheet such as a coated paper is conveyed to the transfer portion as an unfixed sheet, the unfixed sheet is fixed to the unfixed sheet. Slip occurs between the fixing belt 36 and the belt 36, and the driving force of the pressure roller 30 is not transmitted to the fixing belt 36 and the fixing roller 28, so that the driven roller 30 is not driven (rotated). When such a situation occurs, the unfixed sheet stops at the transfer portion and jams, or even if the unfixed sheet can pass through the transfer portion, the unfixed toner on the unfixed sheet is stopped. Is rubbed by the fixing belt 36, and the image is disturbed.

However, in this embodiment, the one-way clutch 60 is connected to the fixing roll 28 and the first driven gear 58.
Therefore, even if the driving force of the pressure roller 30 is not transmitted to the fixing belt 36, the peripheral speed of the fixing roller 28 is lower than the peripheral speed of the first driven gear 58. At the time when it starts to be late, the first driven gear 58 is driven to rotate clockwise in the drawing.
In this way, the unfixed sheet is reliably passed through the contact portion, and the risk of jamming is effectively prevented, and the unfixed toner image is disturbed when passing through the contact portion. Is suppressed.

{Description of Heating Roll 34} Inside the above-described heating roll 34, in this embodiment, an 800 W halogen lamp whose light distribution at both ends is set to be 50% larger than the center is provided as the heat source 32. Have been. The heating roll 34 has a diameter of 30 mm in this embodiment.
Then, the thickness of aluminum pipe core of 3.5mm, thickness 20μ
m, and a collar 66 having a diameter of 30 mm made of heat-resistant resin polyetheretherketone (PEEK) is press-fitted into bearings at both ends, whereby the fixing belt 36 meanders. And leaning are prevented.

{Description of Fixing Belt 36} The fixing belt 36 described above is designed so that the unfixed toner on the unfixed sheet S is preheated to the fixing temperature by heat radiation and can be fixed without giving an excessive amount of heat. 36 has a heat capacity per square cm of 0.002 cal / ° C to 0.025 c
al / ° C. are preferred. For this reason, in this embodiment, the fixing belt 36 has an inner diameter of 60 m.
m, an endless belt body made of polyimide having a thickness of 100 μm, and a heat-resistant elastic release layer of silicone rubber coated on the outer peripheral surface of the belt body with a thickness of 150 μm.

The fixing belt 36 is not limited to being formed of polyimide and silicone rubber. For example, an endless belt body such as a 40 μm nickel electroformed belt and an outer peripheral surface of the belt body are used. And a heat-resistant elastic release layer of silicone rubber coated with a thickness of 150 μm.

{Description of Oil Application Roll 38} The fixing device 10 is provided with an oil application roll 38 for applying a small amount of release oil on the outer peripheral surface of the fixing belt 36. The oil application roll 38 is
A support shaft 38A rotatably supported in an axial fixed state,
A heat-resistant paper layer 38B impregnated with silicone oil is provided on the outer periphery of the support shaft 38A.
Is formed from an iron shaft having a diameter of 8 mm in this embodiment.
It is formed so as to have a roller outer diameter of 22 mm in diameter with the porous fluororesin film 38C of μm mounted. By configuring the oil application roll 38 in this manner, it is possible to apply a small amount of stable oil to the outer peripheral surface of the fixing belt 36.

Incidentally, dirt (toner and the like) adhered to the outer peripheral surface of the fixing belt 36 is transferred and adhered to the outer peripheral surface of the oil application roll 38 to be contaminated. Because of this,
A cleaning brush is in contact with the outer peripheral surface of the oil application roll 38, and the oil application roll 38 is always in contact with the cleaning brush.
Is cleaned to remove dirt attached thereto.

{Description of Mechanism for Applying Tension to Fixing Belt 36} As described above, in this embodiment, as a mechanism for applying tension to the fixing belt 36, the oil application roll 38 is perpendicular to the fixing belt 36. A first coil spring 40 for applying a predetermined tension to the fixing belt 36 by pressing in a state, and urging the heating roll 34 in a direction away from the fixing roll 28 to fix the fixing belt in cooperation with the first coil spring 40. A second coil spring for applying a predetermined tension to the belt;

Here, the first coil spring 40 has a casing 68 that rotatably supports the oil application roll 38.
Is attached to the left cover 20 so as to urge the fixing belt 36 toward the fixing belt 36. That is, the casing 68
The guide rib 70 attached to the side plate 16 supports the fixing belt 36 so as to be able to freely contact and separate from the fixing belt 36. Thus, when the left cover part 20 is opened to the left in the figure,
The first coil spring 40 pressing the casing 68 is removed from the casing 68, whereby the pressing state of the oil application roll 38 against the fixing belt 36 is released. Further, when the left cover portion 20 is rotated rightward in the drawing and closed, the first coil spring 40 presses the casing 68 with the pressing force P2, and the oil application roll 38 applies a predetermined tension to the fixing belt 36. Will be pressed.

On the other hand, the second coil spring 42 is interposed between the left end of the swing lever 22 in the figure and the side plate 16, and in other words, rotates the swing lever 22 clockwise in the figure. Then, the heating roll 3 supported by the swing lever 22
4 is a third pressing force P in a direction away from the fixing roll 28.
3 so as to press it. As a result, a predetermined tension is applied to the fixing belt 36.

That is, the heating roll 34 is biased in a direction away from the fixing roll 28 via the swinging lever 22 by the urging force of the second coil spring 42, whereby the heating roll 34 and the fixing roll 28 The fixing belt 36 stretched endlessly is tensioned to a predetermined tension.

As described above, the first and second coil springs 4
Due to the action of the fixing belt 36, the fixing belt 36 frictionally engages with the pressure roller 30 and rotates, and the fixing roller 28 slips with respect to the fixing belt 36 according to the rotation of the fixing belt 36. It is driven in a stable state without slack.

{Description of Driving Mechanism 52} The driving mechanism 52 for rotatingly driving the above-described pressure roll 30 and the like is provided with the fixing device 10 mounted on an electronic copying apparatus as shown in FIG. A transmission gear 62 meshes with an output gear GE connected to a drive source on the side of the electronic copying apparatus via a gear train (not shown), and is rotationally driven by receiving a driving force from the output gear GE.
And a first driven gear 58 which is always meshed with the transmission gear 62 and connected to the fixing roll 28 via the one-way clutch 60, and is always meshed with the first driven gear and A second driven gear 64 fixed coaxially.

The drive mechanism 52 further includes an idle gear 72 that always meshes with the transmission gear 62 described above.
The idle gear 72 always meshes with a third driven gear 74 coaxially fixed to the lower discharge roller 50, and drives the lower discharge roller 50 to rotate at a speed equal to or higher than the rotation of the pressure roller 30. It is configured to be.

{Other Configurations} Fixing Device 1 of this Embodiment
In addition to the above-described configuration, reference numeral 0 denotes a peeling claw for peeling off the fixed sheet adhered to the outer peripheral surface of the pressure roll 30, as shown in FIG. A paper ejection sensor 78 is provided to detect that the leading end of the fixed sheet has been conveyed between the paper roll 54 (the rolling contact portion).

A first thermistor 80 for detecting the temperature of the fixing belt 36 wound around the outer peripheral surface of the heating roll 34 for controlling the temperature of the heat source 32 built in the heating roll 34, A second thermistor 82 for detecting the temperature of the outer peripheral surface of the portion of the fixing belt 36 wrapped around the outer periphery of the pressure roller 28 and a third thermistor 84 for detecting the temperature of the outer peripheral surface of the pressure roll 30 are shown. And a control circuit for controlling the heat generation of the heat source 32 based on the detection results from the first to third thermistors 80, 82, 84.

{Description of Arrangement Above Heating Roll 34} As described above, in this embodiment, the heating roll 34 is disposed substantially above the fixing roll 28. 28, the guide plate 44 is separated from the fixing belt 36 wound endlessly so that the unfixed sheet conveyed on the guide plate 44 does not contact the fixing belt 36. . In other words, the fixing belt 36 is
This means that the unfixed sheet conveyed above is disposed at a position outside a region where the unfixed sheet may pass.

As described above, the heating roll 34 is connected to the fixing roll 2
8 above, no matter how the unfixed sheet in the middle of conveyance is in a curved posture (curled state),
The unfixed toner carried on the upper surface of the sheet is reliably prevented from coming into contact with the fixing belt 36, and the unfixed toner is guided to the rolling contact portion between the fixing roll 28 and the pressure roll 30 without disturbing the unfixed toner. Can be fixed.

{Description of Configuration Angle of Heating Roll 34} In the fixing device 10 having the above-described configuration, the heating roller 34 is disposed substantially above the fixing roll 28 as described above, thereby achieving a specific effect. Can be done.
Here, in order to clearly define the range “approximately above”, as shown in FIG. 4, an experimental example will be described in which the configuration angle of the heating roll 34 is variously changed and the optimum range is obtained.

First, in this experimental example, a perpendicular passing through the center point of the fixing roll 28 is defined as a base line B.
Is defined as θ, and the line segment L connecting the center points of the fixing roll 28 and the heating roll 34 is defined as θ, the position of the heating roll 34 is changed, and the configuration angle θ becomes 90 ° or more.
At 180 °, the frequency of occurrence of image rubbing at the entrance of the transfer part between the fixing roll 28 and the pressure roll 30 and the frequency of occurrence of abnormalities at the exit of the transfer part are determined during single-sided copying. And at the time of double-sided copying, respectively.

Here, ± of the constituent angle θ is defined as “+” when the value is measured counterclockwise from the base line B, and “−” is defined as the value measured clockwise from the base line B in the figure. Therefore, +1
The heating roll 34 at 80 ° and the heating roll 34 at −180 ° indicate the same position.
The heating roll 34 at 105 ° and the heating roll 34 at −255 ° indicate the same position. on the other hand,
In this embodiment, the abnormality at the outlet of the transfer portion means occurrence of an offset or occurrence of a jam at the outlet of the transfer portion.

The measurement conditions are as follows.

That is, the nip width at the rolling contact portion was set to 8 mm, and the pressing force P1 for this was set to 24 kgf / one side. On the other hand, the temperature of the portion of the fixing belt 36 wound around the fixing roll 28 was set to 160 ° C., and the surface temperature of the pressure roll 30 was set to 140 ° C. Further, the conveyance speed of the unfixed sheet was set to 180 mm / sec, and the pressure roll 30 was driven to rotate in synchronization with the conveyance speed. As the toner, A color toner manufactured by Fuji Xerox Co., Ltd. was used, and as a sheet, plain paper of 64 g / m2 was adopted.

Thus, the constituent angle θ is set to 90 °, 1
05 °, 120 °, 150 °, 180 °, -150 °,
Divided into nine types of -120 °, -105 °, -90 °
The measurement was performed under the measurement conditions described above.

Table 1 shows the measurement results.

[0064]

[Table 1]

As is apparent from Table 1, when the constituent angle θ is larger than 105 ° and smaller than −105 °, that is, when the constituent angle θ is measured only in the counterclockwise direction, When the angle is within the range of from 255 ° to 255 °, there is no occurrence of image rubbing at the entrance of the transfer part and no occurrence of abnormality at the exit of the transfer part, and a good fixing operation is performed. It has been found. On the other hand, when the constituent angle θ is 10
When the angle is 5 ° or less, it was found that either an image rubbing at the entrance of the transfer part or an abnormality at the exit of the transfer part occurred, and good fixing operation was not performed.

As described in detail above, in this embodiment, the heating roll 34 is disposed substantially above the fixing roll 28, and more specifically, the heating roll 34 is positioned at the center point of the heating roll 34 and the center of the fixing roll 28. The line segment L connecting the point is the fixing roll 2
In a state where a line segment connecting the center points of the pressure roller 8 and the pressure roll 30 to each other is set as a base line B, the angle measured from the base line B is about 105
The fixing plate 36 is disposed at a position within the range of about 255 degrees to about 255 degrees, so that the fixing plate 36 wound endlessly between the heating roll 34 and the fixing roll 28 and the guide plate 44 The unfixed sheet conveyed on 44 is separated so as not to contact the fixing belt 36. In other words, the fixing belt 36 is
This means that the unfixed sheet conveyed above is disposed at a position outside a region where the unfixed sheet may pass.

As a result, according to this embodiment, the unfixed sheet in the middle of conveyance may be in any curved posture (curl state) due to a jump or a slack due to a difference in conveyance speed from the transfer unit. The unfixed toner carried on the upper surface of the sheet is reliably prevented from coming into contact with the fixing belt 36, and the unfixed toner is fixed without disturbing the unfixed toner.
To the rolling contact portion between the pressure roller 30 and the pressure roll 30, and it can be reliably fixed.

In this embodiment, the upper fixing roll 28 is formed from an elastic roll, and the lower pressure roll 30 is formed from a roll having a higher on-roller hardness than the fixing roll 28. As compared with the conventional configuration in which the fixing roll is formed of a metal roll, the shape of the nip at the transfer contact portion can easily achieve the state of being recessed downward from the state of being downwardly recessed. As a result, according to this embodiment, a force in the direction in which the fixed sheet is separated from the fixing belt 36 is obtained from the nip shape itself at the rolling contact portion, and the toner is carried on the surface in contact with the fixing belt 36. Even if it is done, the oil application roll 38 for preventing the offset to the fixing belt 36
, The amount of oil applied can be suppressed to a small amount, and even if oil is not used, an offset to the fixing belt 36 side and a fixing operation without a jam can be achieved.

Further, in this embodiment, the upper fixing roll 28 is formed from an elastic roll, and the lower pressing roll 30 is formed from a roll harder than the elastic roll. As compared with the case where both are formed from hard rolls, a state in which the projections are substantially upward from substantially horizontal can be easily achieved. As a result, according to this embodiment, the amount of oil applied by the offset oil application roll 38 can be suppressed to a very small amount, and a fixing operation free from offset and jam can be achieved even without oil.

Further, in this embodiment, a material having a small heat capacity is adopted as the fixing belt 36 as the heat transfer belt, and the winding angle of the fixing belt 36 around the heating roll 34 is large. This means that the fixing belt 36 is in close contact. As a result, according to this embodiment, even if the sheets are fed at a high speed, that is, even if the number of sheets passed per unit time is a large number, it is necessary for the fixing operation at the transfer contact portion between the fixing roll 28 and the pressure roll 30 The temperature can be reliably maintained.

In this embodiment, the heat source is not built in the fixing roll 28 which is configured as an elastic roll, but the heat source 32 is built in the heating roll 34 disposed at a position separated from the fixing roll 28. As a result, the thickness of the silicone rubber heat-resistant elastic body 28B of the fixing roll 28 can be made sufficiently large. As a result, according to this embodiment, the nip width at the rolling contact portion is reduced by the fixing roll 28. Can be made sufficiently wide while maintaining a small diameter.

In this embodiment, the one-way clutch 60 is interposed between the first driven gear 58 and the fixing roller 28, so that the main drive for sheet conveyance (ie, the sheet conveyance speed) is performed. , A pressure roll 30 is set instead of the fixing roll 28. For this reason, for example, the fixing roll 28 is heated during the fixing operation, and as a result, the fixing roll 28 is heated by thermal expansion.
Even if the outer diameter of the sheet expands thermally, the sheet conveying speed is not regulated by the fixing roll 28, so that the sheet conveying speed does not change due to the thermal expansion, and the sheet can always be kept constant. become. As a result, according to the present embodiment, it is possible to maintain the linear velocity constant and reliably prevent transfer deviation, image rubbing, and the like.

[0073]

[Explanation of Modifications] It is needless to say that the present invention is not limited to the configuration of the above-described embodiment, but can be variously modified without departing from the gist of the present invention.

For example, in the above-described embodiment, the case where the fixing apparatus 10 is applied to an electronic copying apparatus has been described. However, the present invention is not limited to such an application, and the electronic facsimile apparatus, It goes without saying that the present invention can be applied to an electronic image forming apparatus such as an electronic printer.

Further, in the above-described embodiment, the description has been made such that the unfixed sheet is conveyed to the fixing device 10 from the lateral direction. However, the present invention is not limited to such a configuration, and the unfixed sheet may be conveyed. The sheet may be configured to be conveyed in a vertical direction, for example, from bottom to top. In this case, the pressure roll 30 is not below the fixing roll 28,
Needless to say, the heating roll 34 is arranged on the side of the fixing roll 28 opposite to the side on which the pressure roll 30 is arranged. .

In the above-described embodiment, the third thermistor 8 for detecting the temperature of the outer peripheral surface of the pressure roll 30 is used.
4 has been described, but it goes without saying that the configuration can be omitted.

In the above-described embodiment, the heat source 32 is described as being disposed inside the heating roll 34. However, the present invention is not limited to such a configuration, and It may be configured to be further provided inside the. In this case, as shown in FIG.
Needless to say, the third thermistor 84 for detecting the temperature of the outer peripheral surface of 0 is indispensable.

[0078]

As described above in detail, according to the present invention, the unfixed toner carried on the recording medium is not disturbed regardless of the curved posture (curl state) of the recording medium being conveyed. A fixing device capable of fixing this is provided.

Further, according to the present invention, there is provided a fixing device in which the recording medium after the completion of the fixing operation is less likely to be offset.

[0080]

[Brief description of the drawings]

FIG. 1 is a front sectional view showing a configuration of an embodiment of a fixing device according to the present invention.

FIG. 2 is a diagram illustrating a state of rolling contact between a fixing roll and a pressure roll.

FIG. 3 is a front view showing a configuration of a driving mechanism.

FIG. 4 is a diagram illustrating a configuration angle in an experimental example performed to check an allowable range of an arrangement position of a heating roll with respect to a fixing roll.

FIG. 5 is a front view schematically showing a configuration of a conventional fixing device.

[Explanation of symbols]

 Reference Signs List 10 Fixing device 12 Housing 14 Bottom plate 16 Side plate 18 Upper cover part 20 Left cover part 22 Swing lever 24 First support shaft 26 Second support shaft 28 Fixing roll 28A Core part 28B Roll body 30 Pressure roll 30A Core metal Unit 30B Roll Body 32 Heat Source 34 Heating Roll 36 Fixing Belt 38 Oil Application Roll 40 First Coil Spring 42 Second Coil Spring 44 Guide Plate 46 Inlet Port 48 Discharge Path 50 Lower Discharge Roll 52 Drive Mechanism 54 Upper Discharge Roll 56 leaf spring 58 first driven gear 60 one-way clutch 62 transmission gear 64 second driven gear 66 collar 68 casing 70 guide rib 72 idle gear 74 third driven gear 76 peeling claw 78 paper ejection sensor 80 first thermistor 82 first 2 thermistor 84 3rd thermistor EB endless belt GE output gear S unfixed sheet

Claims (8)

[Claims] An image forming apparatus comprising: a fixing roll; and a pressure roll which is urged to be in rolling contact with the fixing roll, wherein a sheet having unfixed toner carried on a surface thereof is rotated by the fixing roll and the pressure roll. By passing the contact along one direction,
In a fixing device for fixing the unfixed toner on the sheet, the fixing roll is disposed adjacent to a side opposite to a side on which the pressure roll is disposed, and a heating unit is disposed inside. A heat transfer belt that is endlessly wound around the heating roll and the fixing roll, receives heat from the heating unit, and heats the unfixed toner on the sheet passing through the transfer unit. Wherein the fixing roll is formed from an elastic roll having an elastic layer on the outer periphery. 2. The apparatus according to claim 1, further comprising a driving unit configured to rotationally drive the pressure roll, wherein the heat transfer belt is driven to travel while being frictionally engaged with the pressure roll. The fixing device according to claim 1, wherein the heating roll is driven to rotate. 3. The fixing device according to claim 2, wherein the driving unit rotationally drives the fixing roll at a peripheral speed lower than that of the pressure roll. 4. The fixing roll includes a driven gear mounted coaxially with the fixing roll, the driving unit includes a driving gear meshing with the driven gear, and between the driven gear and the fixing roll. A one-way clutch is provided, wherein the one-way clutch allows rotation of the fixing roll faster than the driven gear, and prohibits rotation of the fixing roll slower than the driven gear. Item 4. The fixing device according to item 3. 5. The fixing roll according to claim 1, wherein the fixing roll includes a cored bar, and an elastic layer disposed on the outer periphery of the cored bar with a predetermined thickness. 3. The fixing device according to claim 1. 6. The fixing device according to claim 1, wherein the pressure roll is formed of a roll that is harder than the hardness of the elastic layer on the roller. 7. The fixing device according to claim 1, wherein the pressure roller is rotatably supported around a fixed axis. 8. The distance between the rotation axis of the pressure roll and the rotation axis of the fixing roll is set shorter than the sum of the radius of the pressure roll and the radius of the fixing roll. The fixing device according to claim 7, wherein