JP6623699B2 - Nip forming unit, fixing device, and image forming device - Google Patents

Description

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

Various sizes of paper are used in image forming apparatuses such as copiers and printers.
If the length of the heater of the fixing device is set to correspond to the maximum size of the paper, when the small size of the paper is passed, the temperature rise at the end portion (non-paper passing portion) becomes large, so that the transport speed of the paper is reduced. Need to reduce productivity.
To cope with this problem, a halogen heater having a dense light distribution at the center and a halogen heater having a dense light distribution near the edges are provided inside the fixing roller. A fixing device that turns on only a halogen heater having a dense light distribution is known.
Although the frequency of use of the entire sheet is extremely small, a large-size (special size) sheet such as an A3-size sheet or a 13-inch sheet slightly larger than the A3-size sheet may be used.
Even if an attempt is made to separately provide a halogen heater having a light distribution corresponding to such a large-sized sheet, it is difficult because the diameter of the fixing roller is restricted due to downsizing.

In Patent Document 1, a nip forming unit is provided inside a thin and flexible endless belt member which quickly rises to a fixing temperature, and a nip forming unit and a pressing member are provided between the belt member and the pressure roller. A fixing device that forms a nip by a contact pressure with a pressure roller is disclosed.
A plurality of halogen heaters having different light distributions are provided inside the belt member.
At both ends in the longitudinal direction of the belt member as the fixing roller, an end heat source that can handle a large-sized sheet is provided at a position upstream of the nip in the rotation direction of the belt member.
The end heat source is provided so as to contact an inner surface or an outer surface of the belt member.
With the configuration in which the end heat source is provided, it is possible to cope with large-sized paper with a simple configuration without adding a halogen heater dedicated to large-sized paper.

In the configuration described in Patent Literature 1, the end of the fixing belt is heated by an end heater at a position upstream of the nip portion in the belt running direction, and the end of the fixing belt flaps during running so that the end of the fixing belt flaps. Since the contact with the section heater is uncertain, a configuration is employed in which the belt end and the end heater are pressed against each other with a predetermined pressure. For this reason, since the pressure is applied to the fixing belt also at other portions of the nip portion, there is a problem that the fixing belt is likely to have a running failure.
Further, there has been a problem that the residual toner not fixed on the conveyed paper is re-melted on the belt member at the position of the end heat source, and this remains as fixed toner.

  The present invention has been made in view of such a situation, and it is possible to obtain good heating efficiency while maintaining stable running of a fixing member, and to contribute to solving a fixing problem due to re-melting of residual toner. The main purpose is to provide a nip forming unit.

According to the first aspect of the present invention , a recording medium is provided inside an endless fixing member which is flexible and rotatably supported, and a recording medium is provided between the fixing member and a facing member facing the fixing member. A nip forming member for forming a nip to be nipped and conveyed; a fixing heat source for heating at least a central portion of a paper passing area in a longitudinal direction of the fixing member; and a fixing heat source provided in the nip forming member. possess an end heat source for heating the inner surface of the end portion in the longitudinal direction, said fixing heat source is provided in a portion excluding the nip forming member, stepped said end heat source positioned near both ends of the nip forming member It is characterized by being attached to a part .

  According to the present invention, it is possible to provide a nip forming unit that can obtain good heating efficiency while maintaining stable running of the fixing member and that contributes to solving the problem of sticking due to re-melting of residual toner. Further, since the end heat source is provided in the nip where the fixing member receives pressure, the location where the fixing member receives pressure can be set to one location, and the possibility that the fixing member becomes poor in running can be reduced. A nip forming unit can be provided.

FIG. 1 is a schematic configuration diagram of a color printer as an image forming apparatus according to a first embodiment of the present invention. It is an outline sectional view of a nip part. It is an outline sectional view of a nip part showing a nip width. FIG. 3 is a perspective view of a main part showing a support structure of a fixing belt. FIG. 4 is a diagram illustrating a positional relationship between a light distribution of a halogen heater and an end heater. It is an exploded perspective view of a nip formation unit. FIGS. 4A and 4B are cross-sectional views of a main part showing a contact state between an end heater and a nip forming member and a fixing belt, wherein FIG. 4A is a diagram of the first embodiment and FIG. FIG. 14 is a cross-sectional view of a main part showing a contact state between an end heater and a nip forming member and a fixing belt according to another modified example, where (a) shows a state before nip formation, and (b) shows a state at the time of nip formation. FIG. FIG. 14 is a cross-sectional view of a main part showing a contact state between an end heater and a nip forming member and a fixing belt in still another modification. 7A and 7B are diagrams illustrating the heat distribution output of the halogen heater according to the second embodiment, in which FIG. 7A is a diagram for explaining a temperature drop at the end of a conventional halogen heater, and FIG. FIG. FIG. 9 is a diagram illustrating a positional relationship between a light distribution of a halogen heater and an end heater according to a second embodiment. FIG. 13 is a diagram illustrating a positional relationship between a light distribution of a halogen heater and an end heater according to a modification of the second embodiment. It is a figure which shows the electricity supply structure of a halogen heater and an end part heater in each embodiment. FIG. 14 is a diagram illustrating an energization pattern in the energization configuration of FIG. 13. It is a figure which shows the modification of the electricity supply structure of a halogen heater and an end heater in each embodiment. FIG. 16 is a diagram illustrating an energization pattern in the energization configuration of FIG. 15. It is a figure explaining a sliding sheet used for each embodiment. It is a figure explaining the end heater used for each embodiment. FIG. 3 is a diagram illustrating a positional relationship between a resistance heating element and a fixing belt used in each embodiment. It is a figure which shows the nip formation unit used for the modification of each embodiment. It is a figure which shows the electricity supply structure of the halogen heater and end heater used for the other modification of each embodiment. FIG. 2 is a diagram illustrating a metal fixing belt used in each embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, before describing this embodiment, a conventional configuration and problems will be described.
When fixing small-size paper, turn on the halogen heater with a dense light distribution at the center, and when fixing large-size paper, use a halogen heater with a dense light distribution near the end together with an appropriate heater. Lights on and off to support paper of various sizes.

Here, regarding the paper size and the frequency of use, most of the normally used paper is up to A3 size, and the A3 size paper is passed in the vertical direction.
Particularly, frequently used sheets of A4 or LT size are often passed in the horizontal direction in order to increase productivity.
For this reason, if the heating width for fixing is about 300 mm, in most cases, 99% or more can be covered depending on the model.
On the other hand, although the frequency of use for the whole is very small, it is required to support a sheet of a size larger than the A3 width, such as A3 nip or 13 inches.

In the case of a heating method using a halogen heater, since a plurality of heaters corresponding to a small size are provided inside a fixing roller having a diameter of about 30 mm, the number of heaters cannot be easily increased. For this reason, the halogen heater having a dense light distribution at the end portion has to be lengthened in accordance with the paper width larger than the A3 width.
As described above, considering the frequency of use, heating with a width of about 300 mm is overwhelmingly predominant. However, when the long halogen heater is used, the heater is heated to about 330 mm width, and the difference in energy consumption is wasted.
Furthermore, the temperature rises near the end of the 330 mm width when the paper is passed in A3 or A4 horizontal (A4Y) size, and it has been necessary to reduce productivity or provide a fan to cool this.
In the case where the reflection plate is provided, there has been a problem that the temperature of the end of the heater abnormally rises.
In order to deal with such a problem, the device described in Patent Document 1 has been proposed.

A first embodiment of the present invention that solves the above-described problem of Patent Document 1 will be described with reference to FIGS.
First, an outline of the configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG.
The image forming apparatus 100 is a tandem-type color printer in which image forming units for forming a plurality of color images are arranged side by side along the moving direction of the intermediate transfer belt.

The image forming apparatus 100 includes a photosensitive drum 20 </ b> Y as an image carrier capable of forming an image corresponding to each of the colors separated into yellow (Y), cyan (C), magenta (M), and black (Bk). , 20C, 20M, and 20Bk.
The toner image as a visible image formed on each of the photosensitive drums 20Y, 20C, 20M, and 20Bk is superimposed on an intermediate transfer belt 11 as an intermediate transfer member that is movable in the direction of arrow A1 while facing each of the photosensitive drums. In addition, the primary transfer is performed.
Thereafter, the toner images are collectively transferred to the sheet S as a recording medium by a secondary transfer process.
Around the photosensitive drums 20, devices for performing image forming processing in accordance with the rotation of the photosensitive drums are arranged.

An apparatus for performing image forming processing will be described on behalf of the photosensitive drum 20Bk for forming a black image.
Around the photosensitive drum 20Bk, a charging device 30Bk for performing image forming processing, a developing device 40Bk, a primary transfer roller 12Bk, and a cleaning device 50Bk are arranged in this order along the rotation direction of the photosensitive drum 20Bk.
After charging by the charging device 30Bk, optical writing based on image information is performed on the surface of the photosensitive drum 20Bk by the optical writing device 8, and an electrostatic latent image is formed.
The electrostatic latent image is visualized as a toner image by the developing device 40Bk.

The toner images formed on the respective photoconductor drums 20 are transferred to the same position on the intermediate transfer belt 11 in the process of moving the intermediate transfer belt 11 in the direction A1.
In the primary transfer, the timing is shifted from the upstream side in the A1 direction to the downstream side by applying a voltage from the primary transfer roller 12 disposed opposite to each photosensitive drum 20 with the intermediate transfer belt 11 interposed therebetween. Done.
The photosensitive drums 20Y, 20C, 20M, and 20Bk are arranged in this color order from the upstream side in the moving direction of the intermediate transfer belt 11.
The photosensitive drums 20Y, 20C, 20M, and 20Bk are provided in image stations for forming yellow, cyan, magenta, and black images, respectively.

The image forming apparatus 100 is provided with four image stations that perform image forming processing for each color, and is disposed above each photosensitive drum 20 so as to face each other. The intermediate transfer belt 11 and the primary transfer rollers 12Y, 12C, 12M, And an intermediate transfer belt unit 10 having 12Bk.
Further, the image forming apparatus 100 includes a secondary transfer roller 5 as a secondary transfer unit that is disposed to face the intermediate transfer belt 11 and rotates following the intermediate transfer belt 11.
Further, the image forming apparatus 100 includes an intermediate transfer belt cleaning device 13 that is disposed to face the intermediate transfer belt 11 and cleans the intermediate transfer belt 11.
The optical writing device 8 is disposed below and facing the four image stations.

The optical writing device 8 includes a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a turning mirror, a rotating polygon mirror as a deflecting means, and the like.
The optical writing device 8 emits writing light Lb corresponding to each color to each photosensitive drum 20 to form an electrostatic latent image on each photosensitive drum 20.
In FIG. 1, for convenience, the writing light Lb is assigned to only the image station for a black image, but the same applies to other image stations.

At a lower portion of the image forming apparatus 100, a sheet feeding device 61 is provided as a sheet cassette in which sheets S conveyed between the respective photosensitive drums 20 and the intermediate transfer belt 11 are stacked.
The sheet S conveyed from the sheet feeding device 61 is moved between the intermediate transfer belt 11 and the secondary transfer roller 5 by the registration roller pair 4 at a predetermined timing corresponding to the timing of forming the toner image by the image station. It is fed out to the next transfer section.
The arrival of the leading end of the sheet S at the registration roller pair 4 is detected by a sensor (not shown).

The sheet S to which the toner image has been transferred is sent to the fixing device 150, where heat and pressure are applied to fix the toner image.
The fixed sheet S is discharged by the discharge roller pair 7 onto the upper surface of the image forming apparatus main body as a discharge tray.
The toner bottles 9Y, 9C, 9M, and 9Bk filled with yellow, cyan, magenta, and black toners are provided below the upper surface of the image forming apparatus main body.

The intermediate transfer belt unit 10 includes, in addition to the intermediate transfer belt 11, the primary transfer rollers 12Y, 12C, 12M, and 12Bk, a drive roller 72 around which the intermediate transfer belt 11 is wound and a driven roller 73.
The driven roller 73 also has a function as a tension urging unit for the intermediate transfer belt 11. Therefore, the driven roller 73 is provided with an urging unit using a spring or the like.
A transfer device 71 includes the intermediate transfer belt unit 10, the primary transfer rollers 12Y, 12C, 12M, and 12Bk, the secondary transfer roller 5, and the intermediate transfer belt cleaning device 13.
The sheet feeding device 61 has the feeding roller 3 that comes into contact with the upper surface of the uppermost sheet S, and the uppermost sheet S is rotated by driving the feeding roller 3 counterclockwise. The sheet is fed toward the registration roller pair 4.

The intermediate transfer belt cleaning device 13 provided in the transfer device 71 has a cleaning brush and a cleaning blade disposed so as to face and contact the intermediate transfer belt 11.
The intermediate transfer belt cleaning device 13 scrapes and removes foreign matter such as residual toner on the intermediate transfer belt 11 with a cleaning brush and a cleaning blade.
The intermediate transfer belt cleaning device 13 also has a discharge unit for carrying out and discarding the residual toner removed from the intermediate transfer belt 11.

The configuration of the fixing device 150 will be described in detail with reference to FIGS.
As shown in FIG. 2, the fixing device 150 includes a fixing belt 14 as a thin and flexible endless fixing member, and a pressure roller 16 as an opposing member disposed opposite to the fixing belt 14. have.
A nip forming unit 18 for forming a nip N for nipping and transporting the sheet S between the fixing belt 14 and the pressure roller 16 is provided inside the fixing belt 14.
The nip forming unit 18 includes a nip forming member 22 disposed inside the fixing belt 14 facing the pressure roller 16, and an end heater as an end heat source integrally provided at both ends of the nip forming member 22. 24, and a stay member 26 for holding the nip forming member 22 against the pressing force from the pressure roller 16.

The nip forming member 22 slides on the inner surface of the fixing belt 14 via the low friction sheet 6 as a sliding sheet as shown in FIG.
By applying a lubricant such as fluorine grease or silicone oil to the low friction sheet 6, the sliding torque can be reduced.
The nip forming member 22 may be configured to directly contact the inner surface of the fixing belt 14 without providing the low friction sheet 6.

The stay member 26 has a box shape with an opening on the side opposite to the nip N side, and halogen heaters 28a and 28b as fixing heat sources are disposed inside the stay member 26.
On the opening side of the stay member 26, the fixing belt 14 is directly heated by radiant heat from the inner surface side by halogen heaters 28a and 28b.

In order to increase the heating efficiency of the halogen heaters 28a and 28b, a plate-shaped reflecting member 31 that reflects light emitted from the halogen heaters 28a and 28b to the fixing belt 14 is provided on the inner surface of the stay member 26.
The reflection member 31 is provided to suppress unnecessary energy consumption due to the stay member 26 being heated by radiant heat from the halogen heaters 28a and 28b.
Similar effects can be obtained by performing heat insulation or mirror finishing on the inner surface of the stay member 26 instead of providing the reflection member 31.

As shown in FIG. 3, the pressure roller 16 has a configuration in which a hollow rubber roller 16a is provided with a silicone rubber layer 16b.
On the surface of the rubber layer 16b, a release layer made of PFA (perfluoroalkoxy fluororesin) or PTFE (polytetrafluoroethylene) having a thickness of 5 to 50 μm is provided to obtain releasability.
The pressure roller 16 is rotated by a driving force transmitted from a driving source such as a motor provided in the image forming apparatus via a gear.
The pressure roller 16 is pressed against the fixing belt 14 by a spring or the like, and the rubber layer 16b of the pressure roller 16 is crushed and deformed to form a predetermined nip width Nw in the paper transport direction. You.

The pressure roller 16 may be a solid roller, but a hollow roller may have a smaller heat capacity. The pressure roller 16 may have a heating source such as a halogen heater inside.
The rubber layer 16b may be made of solid rubber, but if there is no heater inside the pressure roller, sponge rubber may be used.
Sponge rubber is more preferable because the heat insulating property is enhanced and the heat of the fixing belt 14 is hardly deprived.

The fixing belt 14 is a metal belt having a layer thickness of 30 to 50 μm such as nickel or SUS, an endless belt using a resin material such as polyimide, or a film.
The surface layer of the belt has a release layer such as a PFA or PTFE layer, and has a release property so that the toner does not adhere.
Between the base material of the belt and the PFA or PTFE layer, there may be another elastic layer formed of a silicone rubber layer or the like.
When the silicone rubber layer is not provided, the heat capacity is reduced and the fixing property is improved. However, when the unfixed image is crushed and fixed, fine irregularities on the belt surface are transferred to the image, and the fixing unevenness included in the solid portion of the image ( A defect that gloss unevenness) remains.

To improve this, it is necessary to provide a silicone rubber layer of 100 μm or more. Due to the deformation of the silicone rubber layer, fine irregularities are absorbed, and the fixing unevenness is improved.
The fixing belt 14 rotates with the contact friction by the rotation of the pressure roller 16.
The fixing belt 14 is sandwiched and rotated by the nip N, but the other ends are held in a cylindrical shape except for the nip N, and the cross-sectional shape of the fixing belt 14 is stably maintained in a circular shape.
As shown in FIG. 2, a separation member 32 that separates the sheet S from the fixing belt 14 is provided downstream of the nip N in the sheet conveyance direction.

In this embodiment, the shape of the nip N is flat as shown in FIGS. 1 and 3, but the shape of the nip N may be a concave shape which is convex toward the fixing belt 14 side when viewed from the pressure roller 16 side or another shape. You may.
As for the shape of the nip N, when the shape of the nip N is concave, the discharge direction of the leading end of the sheet is closer to the pressure roller 16 and the separability is improved, so that occurrence of jam is suppressed.
In this case, the nip forming surface of the nip forming member 22 is formed in a concave shape. In this case, the contact surfaces of the end heaters 24a and 24b provided integrally with the nip forming member 22 also extend along the nip forming surface. It may be shaped.

The stay member 26 functions to prevent the nip forming member 22 from receiving the pressure from the pressure roller 16 and to obtain a uniform nip width in the axial direction.
In the present embodiment, the nip N is formed by pressing the pressing roller 16 toward the fixing belt 14. However, the nip N may be formed by pressing the nip forming unit 18 toward the pressing roller 16. Good.
The stay member 26 has a sufficient bending strength to support the nip forming member 22, and is made of a metal material such as stainless steel or iron, or a metal oxide such as ceramics.

As shown in FIG. 4, the fixing belt 14 is rotatably supported at both ends in the axial direction by a flange 36 as a supporting member projecting from the side plate 34 in the axial direction. FIG. 4 shows the support structure on one side in the axial direction of the fixing belt 14, but the other side has the same configuration.
The flange 36 that guides both ends of the fixing belt 14 has an outer diameter substantially equal to the inner diameter of the fixing belt 14, and has a length of 5 to 10 mm inside from both ends of the fixing belt 14.
The fixing belt 14 is guided by the flange 36, so that its cross-sectional shape is maintained in a circular shape even during traveling (during rotation).
A portion corresponding to the nip N of the flange 36 is opened to arrange the nip forming unit 18 at a predetermined position.
The stay member 26 has a length extending over the entire axial direction of the fixing belt 14, and is supported with both sides fixed to the side plate 34 and positioned.

As shown in FIG. 5, the halogen heater 28a is a small-sized halogen heater having a dense light distribution at the center in the longitudinal direction of the fixing belt 14.
The halogen heater 28b is a halogen heater corresponding to a size such as an A3 size in which the light distribution at both ends in the longitudinal direction is dense.
When the sheet S is of a small size, only the halogen heater 28a is turned on, and the non-sheet passing portion is prevented from being unnecessarily heated.

The difference between the width of the A3 size or the width of the A4Y in which the A4 size is set in the horizontal direction, and A3 nobi (329 mm) and 13 inches (330 mm) is 32 to 33 mm.
Therefore, if a method of heating only the both ends in the axial direction of the fixing belt 14 is used, if the ends can be heated by a half of the above-mentioned width of 16 to 16.5 mm, as shown in FIG. The width for paper spreads.
In other words, if a portion where the light distribution is not dense at the end of the halogen heater 28b can be heated, it is possible to cope with a large-sized sheet such as an A3-size sheet.
Therefore, the end heaters 24a and 24b need only be as small as about 20 mm in the axial direction.

When passing a large-size sheet such as A3 paper or 13 inches, the halogen heaters 28a and 28b and the end heaters 24a and 24b are energized.
When a sheet of A3 size or smaller is passed, only the halogen heaters 28a and 28b or the halogen heater 28a are energized, and the end heaters 24a and 24b are not energized.
If the halogen heater 28b has a heating structure capable of handling large-size paper such as A3 paper, even if the large-size paper is not passed, that portion is heated and wasteful energy is consumed. .
According to the configuration of the present embodiment, the above problem can be solved by adding a simple configuration in which end heaters 24a and 24b are added at both ends or near both ends of the fixing belt 14.

As shown in FIG. 6, two protrusions 26 b and 26 c extending in the longitudinal direction of the fixing belt 14 are formed on a side surface 26 a of the stay member 26 on the side of the pressure roller 16.
The rectangular parallelepiped nip forming member 22 is housed and positioned between the ridges 26b and 26c, and is fixed to the side surface 26a by means such as bonding.
At both ends in the longitudinal direction of the nip forming member 22, concave portions 22a and 22b as step portions are formed, and end heaters 24a and 24b are housed therein and fixed by means such as bonding.
The surface of the nip forming member 22 facing the pressure roller 16 is a nip forming surface 22c.

Here, the end heaters 24a and 24b will be described. The end heaters 24a and 24b used in this embodiment are the same, and FIG. 18 shows the end heater 24a as a representative.
The end heater 24a is formed by patterning a resistance heating element 52 as a heating member on a ceramic base material 51 having an outer shape of about 10 mm × 20 mm, and laminating an insulating layer 53 of a thin glass layer on the pattern. A terminal 54 connected to a power supply and a switching element is provided at an end of the end heater 24a.

As described above, the end heaters 24a and 24b have the resistance heating element 52 on one surface side, and one surface side having the resistance heating element 52 mainly generates heat and the other surface side has little heat. It is configured so that heat does not reach.
The end heaters 24a, 24b used in the present embodiment have a resistance heating element 52 on the side in contact with the recesses 22a, 22b, and terminals 54 are provided on the surface side.
As shown in FIG. 19, the end heaters 24a and 24b are provided with a resistance heating element 52 on the side not in contact with the fixing belt 14, so that even if the insulating layer 53 is damaged, the power supplied is fixed. Is configured not to reach. In particular, when the fixing belt 14 is made of a metal as described later, the metal in the fixing belt may adversely affect other components in the image forming apparatus, for example, a contact thermistor for a known fixing belt. Increase. Therefore, the above-described configuration is more suitable for securing the creepage distance between the fixing belt 14 and the resistance heating element 52.

As shown in FIG. 7A, the surfaces of the end heaters 24a and 24b that come into contact with the inner surface of the fixing belt 14 and the nip forming surface 22c are in a direction indicated by an arrow F (a drag direction) that is a direction in which the inner surface of the fixing belt 14 is pushed. ) Are the same height.
In other words, the surfaces of the end heaters 24a and 24b that come into contact with the inner surface of the fixing belt 14 are extended surfaces of the nip forming surface 22c in the longitudinal direction.
In the present embodiment, the end heaters 24a and 24b are integrally provided on the nip forming member 22 necessary for forming the nip. Therefore, the end heaters 24a and 24b are arranged inside the fixing belt 14 in a space-saving manner. it can.

In addition, since the surfaces of the end heaters 24a and 24b that contact the inner surface of the fixing belt 14 and the nip forming surface 22c are located at the same height (on the same plane), a sufficient pressing force by the pressure roller 16 is applied. It is added between the belt 14 and the end heaters 24a and 24b.
As a result, the belt can be run in a state where the fixing belt 14 and the end heaters 24a and 24b are in close contact with each other, and good heating efficiency by the end heaters 24a and 24b can be maintained by improving heat transfer.
Since the heating part of the fixing belt 14 by the end heaters 24a and 24b exists in the nip area, there is no problem of re-melting of the untransferred toner due to heating at a part different from the nip as in Patent Document 1.

Further, since the pressing roller 16 also serves as an urging means for bringing the end heaters 24a and 24b into close contact with the fixing belt 14 in order to improve the heat transfer property, there is no need to press only the end heater. Thus, the configuration is simpler than the configuration of Patent Document 1.
In other words, since the end heaters 24a, 24b and the fixing belt 14 are brought into close contact with each other by using the pressing force for forming the nip, the running performance and the poor heat transfer in the configuration as in Patent Document 1 are not satisfied. There is no trade-off problem.

  In the present embodiment, the shape of the concave portion formed in the nip forming member 22 is a shape having an open end in the axial direction. However, as shown in FIG. Is also good. Further, a configuration may be adopted in which the front and rear portions in the axial direction are closed, and both sides orthogonal to the axial direction are open.

As shown in FIG. 8, the end heaters 24a and 24b may be supported by the elastic member 38 in the concave portions 22a and 22b of the nip forming member 22.
In this configuration, as shown in FIG. 8A, when the pressing force from the pressing roller 16 is not applied, the surfaces of the end heaters 24a and 24b that contact the inner surface of the fixing belt 14 and the nip forming surface 22c are different from each other. Not at the same height.
However, as shown in FIG. 8B, when a nip is formed by applying a pressing force by the pressure roller 16, the elastic member 38 is deformed and comes into contact with the inner surface of the fixing belt 14 of the end heaters 24a and 24b. The surface has the same height as the nip forming surface 22c.
As the elastic member 38, a rubber-based material or a spring can be used.

As described above, since the end heaters 24a and 24b are fixedly positioned on the nip forming member 22 as a separate member, the contact surfaces of the end heaters 24a and 24b with the inner surface of the fixing belt 14 and the nip forming surface 22c are formed. The height may shift at the assembly stage.
Even in such a case, if the end heaters 24a and 24b are configured to be supported by an elastic member, manufacturing errors can be absorbed and the surface height can be made the same during nip formation.

In the present embodiment, the end heaters 24a and 24b are provided integrally with the nip forming unit 18, but the present invention is not limited to this.
As shown in FIG. 9, the end heaters 24a and 24b may be provided in the nip area independently of the nip forming unit.
For example, a configuration in which the support members 42a and 42b are fixed to the side plate 34 can be employed.
Also in this case, the surfaces of the end heaters 24a and 24b that contact the inner surface of the fixing belt 14 and the nip forming surface 22c are set at the same height.
Also in this example, the end heaters 24a and 24b may be configured to be displaced by an elastic member.

  In this embodiment, the stay member 26 and the halogen heaters 28a and 28b are integrally provided as a nip forming unit. 4 is a nip forming unit according to the invention.

The end heaters 24a and 24b in the present embodiment may have PTC characteristics. With the PTC characteristic, the resistance value increases at a temperature higher than the set temperature, so that the temperature does not rise above the set temperature. This makes it possible to realize a safe fixing device without fear of burning or breakage of the belt.
Further, in the present embodiment, since the end heaters 24a and 24b are provided inside the fixing belt 14, the belt end can be heated from the inside without hindering the rotation of the fixing belt 14.
Furthermore, if the portions of the end heaters 24a and 24b that come into contact with the inner surface of the fixing belt 14 are made of another smooth material, the sliding resistance can be kept low, and the running of the belt can be kept stable.

According to the above-described configuration, the nip forming unit 18 provided inside the fixing belt 14 includes the nip forming member 22 and the halogen heaters 28a and 28b that heat at least the central portion of the paper passing area in the longitudinal direction of the fixing belt 14. The nip forming member 22 has end heaters 24 a and 24 b for heating the inner surface of the fixing belt 14 at the longitudinal end.
With this configuration, since the end heaters 24a and 24b are provided in the nip N to which the fixing belt 14 receives pressure, the location where the fixing belt 14 receives pressure can be set to one location. It is possible to provide a nip forming unit capable of reducing the possibility of occurrence. Thus, it is possible to provide a fixing device capable of continuously performing a good image forming operation and an image forming apparatus including the fixing device.

A second embodiment will be described with reference to FIGS. The same parts as those of the above-described embodiment are denoted by the same reference numerals, and the description of the already-explained configuration and function will be appropriately omitted.
In the case of the method of heating with a halogen heater, as shown in FIG. 10A, the heat distribution output decreases at the end of the heater in the longitudinal direction.
Regarding the heat distribution output of the halogen heater 28a, the heat distribution output at both ends is trapezoidal, and the output is reduced at the extreme end. This is because there is a boundary between a portion where the light distribution is dense and a portion where the light distribution is sparse at the extreme end, which is a characteristic characteristic of the halogen heater.
For this reason, in the case of A3 size paper, the edges cannot be sufficiently heated, and a fixing failure may occur.

In order to heat the sheet to the end in the longitudinal direction of the sheet width, it is necessary to make the length of the light emitting portion (the portion having a dense light distribution) of the halogen heater longer than the sheet width.
However, in such a case, a temperature rise in the non-sheet passing portion is unavoidable when the sheet is continuously passed.
In order to solve this problem, measures have been taken to provide a member for blocking extra light emitted from the elongated portion of the halogen heater in the non-sheet passing portion, but an excessive amount of the light blocking member during continuous sheet passing has been observed. There is a problem that a temperature rise occurs.
Further, the fact that the halogen heater must emit light to the non-sheet passing portion requires more energy than necessary, which is not desirable from the viewpoint of energy saving.

In the present embodiment, in order to solve the above problem, as shown in FIG. 11, the end heaters 24a and 24b are formed such that at least a part of the heating range in the longitudinal direction is the end in the same direction of the heating range of the halogen heater 28b. They are arranged to overlap.
In other words, the end heaters 24a and 24b are arranged so as to complement a portion where the heat distribution output of the halogen heater 28b is reduced.
According to this configuration, as shown by hatching in FIG. 10B, the reduced portion of the heat distribution output of the halogen heater 28b is complemented by the heating of the end heaters 24a and 24b.
The end heaters 24a and 24b are heaters for compensating for the portion where the heat distribution output is reduced at the extreme end of the halogen heater 28b, and therefore may be small heaters of about 20 mm in length.
According to the configuration of the present embodiment, the above problem can be solved by adding a simple configuration in which the end heaters 24a and 24b are added to both ends or the vicinity of the ends of the fixing belt 14.

During the first period of continuous paper passing immediately after warm-up when the fixing belt 14 and the pressure roller 16 are not sufficiently warmed, the halogen heaters 28a and 28b and the end heaters 24a and 24b are energized.
When the fixing belt 14 and the pressure roller 16 have sufficiently warmed and the temperature drop at the ends has decreased, only the halogen heaters 28a and 28b or the halogen heater 28a are energized, and the end heaters 24a and 24b are not energized.
By performing the heating control in this manner, the temperature rise phenomenon in the non-sheet passing portion can be minimized, and the fixing belt is not heated more than necessary, which is efficient and energy saving.

As shown in FIG. 12, the length of the end heaters 24a and 24b is set to a size that complements the portion where the heat distribution output is reduced at the extreme end of the halogen heater 28b and that can be used for a sheet of A3 size or the like. It may be.
Further, the end heaters 24a and 24b are not limited to a paired arrangement at both ends, but may be a plurality of pairs according to various paper sizes.
The end heaters 24a and 24b may be provided further axially outward than the halogen heater 28b. In such a case, it is possible to cope with a larger number of paper sizes, and it is possible to perform heating with high accuracy, which is more desirable.

When heaters having PTC characteristics are used as the end heaters 24a and 24b, it usually takes longer to raise the temperature than when a halogen heater is used.
For this reason, if the end heaters 24a and 24b and the halogen heaters 28a and 28b are heated at the same time, only the inner side on the center side is heated first, and wasteful energy is consumed.
Further, when heat is removed by passing the paper, the heating time for returning to the target temperature is longer for the end heaters 24a and 24b than for the halogen heater due to the characteristics of PTC.

Therefore, by reducing the productivity in accordance with the heating cycle of the end heaters 24a and 24b, it is possible to perform heating control without temperature variation between the center and the end.
That is, when the end heaters 24a and 24b for heating both ends or the vicinity of both ends of the fixing belt 14 are used, the halogen heaters 28a and 28b corresponding to other normal size paper are heated and controlled according to the temperature rise of the ends. I do.
As a result, when the amount of heat generated by the end heaters 24a and 24b is low, only the heater heating section corresponding to the normal size paper is heated first, so that unnecessary consumption of energy can be prevented.
Further, the transport speed when transporting paper of a size using the end heater is set lower than the transport speed of paper of other sizes.
In this manner, by reducing the productivity of large-sized paper sheets that are not frequently used, the heaters at both ends (end heaters 24a and 24b) can be simplified or reduced in cost, and the efficiency can be improved.

  In the present embodiment, a configuration having two halogen heaters as a fixing heat source has been described. However, the present invention is not limited to this, and a configuration having three or more halogen heaters for small-size paper may be used.

FIG. 20 shows a modification of the nip forming unit.
The nip forming unit 63 includes the nip forming member 22, end heaters 24 a and 24 b, and a stay member 64 that holds the nip forming member 22 against the pressing force from the pressure roller 16.
The stay member 64 integrally has a receiving portion 64a configured similarly to the stay member 26 for receiving the nip forming member 22, and a leg portion 64b having a substantially triangular cross-sectional shape.
Halogen heaters 28a and 28b as fixing heat sources for directly heating the fixing belt 14 from the inner surface side by radiant heat are disposed between the leg portions 64b and the fixing belt 14.
In order to increase the heating efficiency of the halogen heaters 28a and 28b, a reflecting member 65 made of an arc-shaped plate that reflects the light emitted from the halogen heaters 28a and 28b to the fixing belt 14 includes a leg 64b and the halogen heaters 28a and 28b. It is provided between.

Even when the nip forming unit 63 described above is used in place of the nip forming unit 18, the same operation and effect as in the above-described embodiment can be obtained.
Instead of providing the reflection member 65, heat insulation or mirror finishing may be performed on the outer surface of the leg portion 64b. In this case, the heating efficiency is slightly reduced as compared with the case where the reflection member 65 is provided.

Here, the metal fixing belt will be described. The fixing belt 14 shown in FIG. 2, FIG. 17, FIG. 19, and FIG. 20 is driven by the rotation of the pressure roller 16 which is in contact with the outer peripheral surface thereof, and conveys the heat from the heat source toward the nip N. In the fixing device having such a configuration, a load applied to the fixing belt 14 is large, and a resin material such as polyimide may have insufficient strength.
For this reason, a metal material having excellent strength, such as stainless steel, nickel, aluminum, or copper, is often used as a base material of the fixing belt 14.

As schematically shown in FIG. 22, a base material 46 containing a metal material is used, an elastic layer 47 is formed on the outer peripheral surface thereof, and a release layer 48 is formed on the outer peripheral surface thereof by a known method. The illustrated fixing belt 14 can be configured.
Here, the performance required for the base material 46 includes durability, flexibility when forming the fixing belt 14, and heat resistance enough to withstand use at the fixing temperature, and the elastic layer 47 and the release layer 48 It is formed so as to satisfy these performances.
Further, as the base material 46 of the fixing belt 14, nickel is more suitable than stainless steel. This is because the strength is high, the durability is excellent, and the endless belt is easily manufactured by the electroforming process.

13 to 16 show the electrical connection configuration between the halogen heater 28 and the end heater 24 in each of the above embodiments.
When the sheet is conveyed on the basis of the center, the end heaters 24a and 24b are always energized at the same time, so that the end heaters 24a and 24b are electrically connected in series to the power supply 44 as shown in FIG.
With such a connection configuration, electrical control is simplified as compared with a configuration in which the end heaters 24a and 24b are individually turned on and off.
Also, when one end heater breaks down, the electrical connection between the two can be cut off at the same time, and safety can be ensured.
The halogen heater 28a is turned on / off by a switch SW1, the halogen heater 28b is turned on / off by a switch SW2, and the end heaters 24a and 24b are turned on / off by a switch SW3.

When passing small-sized paper, only the halogen heater 28a is energized as shown in FIG. When passing A3 size paper, both halogen heaters 28a and 28b are energized as shown in FIG.
When a sheet of a size larger than the A3 size is passed, the halogen heaters 28a and 28b and the end heaters 24a and 24b are simultaneously energized as shown in FIG.

By independently controlling the heating of the halogen heaters 28a and 28b as heat sources of the non-nip portion for heating the opposite side of the nip portion and the end heaters 24a and 24b, the temperature control at the end portion in the longitudinal direction can be further improved. Can be done with precision.
In addition, it is possible to avoid an increase in the temperature of the non-sheet passing portion.

Heating by the end heaters 24a and 24b is performed when a sheet of a size larger than the A3 size is passed. At this time, the halogen heaters 28b for heating both ends are simultaneously turned on.
Therefore, as shown in FIG. 15, the same effect can be obtained by providing a wiring connecting the halogen heater 28b in series with the end heaters 24a and 24b and controlling the power supply while switching the paths by the switches SW1 and SW4. Can be.
In this way, the control device can be further simplified.
Here, since the halogen heater 28b and the end heaters 24a and 24b have different temperature characteristics, the temperatures of both are adjusted by switching the paths.

When a small-sized sheet is passed, only the halogen heater 28a is energized as shown in FIG. In this case, the switch SW4 is set at a position where it does not come into contact with any of the terminals of the halogen heater 28b and the end heaters 24a and 24b.
When passing A3 size paper, both halogen heaters 28a and 28b are energized as shown in FIG.
When a sheet having a size larger than the A3 size is passed, the halogen heaters 28a and 28b and the end heaters 24a and 24b are simultaneously energized as shown in FIG.
In FIGS. 13 and 15, the wiring connecting the halogen heater 28b and the end heater 24 in series is illustrated. However, in the case of a large-size sheet, the halogen heater 28a is also turned on at the same time. A similar effect can be obtained with a wiring connecting the heater 24 in series.

FIG. 21 is a circuit diagram showing an electrical connection configuration between the halogen heater 28 and the end heater 24 used in another modification of the above embodiment.
In the configuration shown in FIG. 21, the end heater 24a and the end heater 24b are connected in parallel. Therefore, when the switch SW3 is off, no current flows because only the negative electrodes are connected to the end heaters 24a and 24b.
When the switch SW3 is turned on, plus electrodes are connected to the end heaters 24a and 24b, respectively, and electric power from the power supply 44 is supplied to the end heaters 24a and 24b, respectively, so that the end heaters 24a and 24b generate heat.
With such a configuration, when one end heater is short-circuited, a thermal runaway due to an overcurrent can be prevented by adding a fuse (not shown), and safety can be improved.

As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to such specific embodiments, and unless otherwise specified in the above description, the present invention described in the claims is not limited thereto. Various modifications and changes are possible within the scope of the gist.
The effects described in the embodiments of the present invention merely exemplify the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

14 Fixing member (fixing belt)
16 Opposing member (pressure roller)
18 Nip forming unit 22 Nip forming member 22c Nip forming surface 24a, 24b End heat source (end heater)
28a, 28b Fixing heat source (halogen heater)
Reference Signs List 100 image forming device 150 fixing device S recording medium (paper)

JP 2014-178370 A

Claims (16)

A nip is provided inside a flexible and rotatably supported endless fixing member for nipping and transporting a recording medium between the fixing member and an opposing member facing the fixing member. A nip forming member for
A fixing heat source that heats at least a central portion of the paper passing area in the longitudinal direction of the fixing member,
Provided in the nip forming member, it possesses an end heat source for heating the inner surface of the end portion in the longitudinal direction of the fixing member,
The nip forming unit, wherein the fixing heat source is provided in a portion other than the nip forming member, and the end heat sources are attached to step portions located near both ends of the nip forming member . The nip forming unit according to claim 1,
A nip forming unit having a nip forming surface in contact with the inner surface, wherein the nip forming surface is provided at the same height as a surface of the end heat source that heats the inner surface. The nip forming unit according to claim 1,
A nip forming surface in contact with the inner surface, and a plurality of the end heat sources, and a surface facing the fixing member includes a first end heat source, a nip forming surface, and a second end from a longitudinal end. A nip forming unit configured to be arranged in the order of the partial heat sources. The nip forming unit according to claim 2,
A nip forming unit, wherein the nip forming surface contacts the inner surface via a sliding sheet. The nip forming unit according to claim 2,
The nip forming unit, wherein the end heat source is capable of contacting an inner surface of the fixing member, and a surface of the end heat source that contacts the inner surface is disposed within an extension of the nip forming surface. . The nip forming unit according to claim 2,
A nip forming unit, wherein the nip forming surface is provided at the same height as a surface for heating the inner surface of the end heat source at the time of nip forming. The nip forming unit according to any one of claims 1 to 6 ,
The nip forming unit , wherein the end heat source is arranged such that at least a part of a heating range in the longitudinal direction overlaps an end of the fixing heat source in the same direction of a heating range . The nip forming unit according to any one of claims 1 to 7,
The nip forming unit, wherein the end heat source is arranged such that at least a part of a heating range in the longitudinal direction overlaps a portion where a heat distribution output of the fixing heat source is reduced . An endless fixing member that is flexible and rotatably supported,
An opposing member opposing the fixing member,
A nip forming member for forming a nip for nipping and conveying a recording medium between the fixing member and the facing member,
A fixing heat source provided at a portion other than the nip forming member and heating at least a central portion of a paper passing area in a longitudinal direction of the fixing member;
An end heat source attached to a stepped portion located near both ends of the nip forming member and configured to heat an inner surface of an end in the longitudinal direction of the fixing member. The fixing device according to claim 9,
The fixing device according to claim 1, wherein the nip forming member has a nip forming surface that contacts the inner surface, and the nip forming surface is provided at the same height as a surface of the end heat source that heats the inner surface . The fixing device according to claim 10,
The fixing device according to claim 1, wherein the nip forming surface is provided at the same height as a surface of the end heat source that heats the inner surface when the nip is formed . An endless fixing member that is flexible and rotatably supported,
An opposing member opposing the fixing member,
A nip forming member for forming a nip for nipping and conveying a recording medium between the fixing member and the facing member, and at least a paper passing area in a longitudinal direction of the fixing member provided at a portion excluding the nip forming member. A fixing heat source that heats a central portion, and an end heat source that is attached to a step portion located near both ends of the nip forming member and heats an inner surface of an end portion in the longitudinal direction, and inside the fixing member. A nip forming unit provided,
9. The fixing device according to claim 1, wherein the nip forming unit is a nip forming unit . An image forming apparatus comprising the fixing device according to claim 9. The image forming apparatus according to claim 13,
When the size of the recording medium is large enough to use the end heat source, the heating control by the fixing heat source is performed in accordance with a rise in the temperature of the end of the fixing member . The image forming apparatus according to claim 13 ,
When the size of the recording medium is large enough to use the end heat source, the conveyance speed of the recording medium is made slower than that of a recording medium having a smaller size than the recording medium. apparatus. The image forming apparatus according to claim 13 ,
An image forming apparatus , wherein heating of the end heat source and the fixing heat source are controlled independently .

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