JP2023041170A - Fixing device and image forming apparatus - Google Patents

Abstract

To reduce the likelihood of the occurrence of a trouble of causing excessive temperature increase of a portion in a width direction of a fixing member where a nip part is not formed, even if the fixing member and a pressure member are moved in the width direction to vary a length in the width direction of the nip part.SOLUTION: A fixing device is provided with a moving mechanism 55 that moves a fixing roller 21 toward one end in a width direction or the other end in the width direction without moving a central heater 25 and an end heater 26 in the width direction, and moves a pressure roller 31 toward one end in the width direction or the other end in the width direction. In maximum size conveyance in which a sheet P1 with the maximum size is conveyed, the moving mechanism 55 moves the fixing roller 21 and the pressure roller 31 so that a nip part is formed at least within a maximum width direction range M, and in small size conveyance in which a sheet P2 with a size substantially equivalent to a width direction central part N is conveyed, moves the fixing roller 21 and the pressure roller 31 so that the nip part is formed only within a width direction range substantially the same as the width direction central part N.SELECTED DRAWING: Figure 4

Description

The present invention relates to a fixing device that heats a toner image to fix it on the surface of a sheet, and an image forming apparatus having the fixing device, such as a copier, printer, facsimile machine, or a multi-function machine of these.

2. Description of the Related Art Conventionally, in a fixing device in an image forming apparatus such as a copier or a printer, a technique of moving a fixing member (fixing roller) or a pressure member (pressure roller) in the width direction at a predetermined timing is known (for example, , see Patent Document 1).

Specifically, in the fixing device, a pressure member (pressure roller) is pressed against a fixing member (fixing roller) to form a nip portion (fixing nip) through which a sheet (paper) is conveyed. The fixing member is heated by a heater controlled based on the detection result of a temperature sensor that detects the surface temperature of the fixing member. Then, the toner image on the sheet conveyed to the nip portion is fixed on the sheet by the heat received from the fixing member and the pressure of the nip portion.

On the other hand, in Japanese Patent Laid-Open No. 2002-100003, for the purpose of suppressing the problem of wrinkles on the sheet, a press contact portion between a heating rotating body (fixing member) and a pressurizing rotating body (pressure member) is adjusted according to the size of the sheet. A technique for changing the width of the (nip portion) is disclosed.

In a conventional fixing device, when the length of the nip portion in the width direction is changed by moving the fixing member and the pressure member in the width direction, the nip portion is formed in the fixing member by a heater that heats the fixing member in the width direction. Along with the widthwise portion to be formed, the widthwise portion not forming the nip portion was also heated. As a result, there has been a problem that the widthwise portion of the fixing member where the nip portion is not formed (non-sheet-passing region) is excessively heated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems. To provide a fixing device and an image forming apparatus in which the temperature of a portion in the width direction, which does not form a part, is less likely to occur.

The fixing device according to the present invention includes a fixing member that heats a toner image to fix it on the surface of a sheet, a pressure member that presses against the fixing member to form a nip portion where the sheet is conveyed, and a maximum conveyable toner image. a central heater capable of heating the fixing member only in a widthwise central portion of the maximum widthwise range of a sheet of the same size as a heating range; end heaters capable of heating the fixing member with all or part of the fixing member as a heating range; a moving mechanism for moving the pressing member to the other widthwise end and moving the pressing member to the other widthwise end or the one widthwise end; At the time of size conveyance, the fixing member and the pressure member are moved so that the nip portion is formed at least in the maximum width direction range, and a sheet having a size substantially equal to the width direction central portion is conveyed. The fixing member and the pressure member are moved so that the nip portion is formed only in the width direction range substantially equal to the width direction center portion when the small size sheet is conveyed.

According to the present invention, even if the length of the nip portion in the width direction is changed by moving the fixing member and the pressure member in the width direction, the temperature of the portion of the fixing member in the width direction that does not form the nip portion is excessively increased. Therefore, it is possible to provide a fixing device and an image forming apparatus that are less likely to cause the problem of the image forming apparatus.

1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention; FIG. 2 is a configuration diagram showing a fixing device; FIG. 5 is a schematic diagram showing the positional relationship in the width direction between the center heater and the end heaters with respect to the fixing roller; FIG. (A) a schematic diagram showing the positional relationship in the width direction between the fixing device and the sheet when conveying a large size; (B) a schematic diagram showing the positional relationship in the width direction between the fixing device and the sheet when conveying a small size; is. FIG. 10 is a schematic diagram showing a fixing device when conveying a small size sheet in Modification 1; FIG. 11 is a schematic diagram showing a fixing device when conveying a small size sheet in modification 2; (A) Schematic diagram showing the fixing device when conveying a large size sheet, (B) Schematic diagram showing the fixing device when conveying a medium size sheet, and (C) Schematic diagram showing the fixing device when conveying a small size sheet in modification 3 Figure and.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant description thereof will be appropriately simplified or omitted.

First, the overall configuration and operation of the image forming apparatus 1 will be described with reference to FIG.
In FIG. 1, 1 is a tandem type color copier as an image forming apparatus, 2 is a writing unit that emits laser light based on input image information, 3 is a document conveying unit that conveys a document D to a document reading unit 4, and 4 is a document reading unit. A document reading unit for reading image information of a document D is shown.
Reference numeral 7 denotes a paper feeding unit in which sheets P such as paper are stored; 9, registration rollers (timing rollers) for adjusting the conveying timing of the sheets P; 1 shows a photosensitive drum on which a black toner image is formed.

A charging unit 12 charges the surfaces of the photosensitive drums 11Y, 11M, 11C and 11BK, and a developer 13 develops the electrostatic latent images formed on the surfaces of the photosensitive drums 11Y, 11M, 11C and 11BK. 14 is a primary transfer roller for superimposing and transferring the toner images formed on the surfaces of the photosensitive drums 11Y, 11M, 11C and 11BK onto the surface of the sheet P; 15 is the photosensitive drums 11Y, 11M and 11C; 11 shows a cleaning section for collecting untransferred toner remaining on the surface of 11BK.
16 is an intermediate transfer belt cleaning unit for cleaning the intermediate transfer belt 17; 17 is an intermediate transfer belt onto which toner images of a plurality of colors are superimposed and transferred; A secondary transfer roller for transferring, and 20 denotes a fixing device for fixing the toner image (unfixed image) on the sheet P. FIG.

An operation (printing operation) in normal color image formation in the image forming apparatus will be described below.
First, the document D is conveyed from the document platen by the conveying rollers of the document conveying section 3 and placed on the contact glass 5 of the document reading section 4 . Then, the document reading unit 4 optically reads the image information of the document D placed on the contact glass 5 .

Specifically, the document reading unit 4 scans the image of the document D on the contact glass 5 while irradiating the light emitted from the illumination lamp. Then, the light reflected by the document D forms an image on the color sensor via the mirror group and the lens. The color image information of the document D is read by the color sensor for each color separation light of RGB (red, green, blue), and then converted into an electrical image signal. Further, based on the RGB color-separated image signals, the image processing unit performs color conversion processing, color correction processing, spatial frequency correction processing, and the like to obtain yellow, magenta, cyan, and black color image information.

Image information for each color of yellow, magenta, cyan, and black is sent to the writing section 2 . Laser light (exposure light) based on the image information of each color is emitted from the writing unit 2 toward the surfaces of the corresponding photosensitive drums 11Y, 11M, 11C, and 11BK.

On the other hand, the four photosensitive drums 11Y, 11M, 11C, and 11BK rotate counterclockwise in FIG. First, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK are uniformly charged at the portions facing the charging section 12 (charging step). In this way, charging potentials are formed on the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK.
After that, the surfaces of the charged photoreceptor drums 11Y, 11M, 11C, and 11BK reach respective laser light irradiation positions (exposure step). Specifically, in the writing unit 2, four light sources emit laser beams corresponding to image signals corresponding to respective colors. Each laser beam passes through a different optical path for each of the yellow, magenta, cyan, and black color components.

A laser beam corresponding to a yellow component is irradiated onto the surface of the first photosensitive drum 11Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction, width direction) of the photosensitive drum 11Y by the polygon mirror rotating at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11Y after being charged by the charging section 12. FIG.

Similarly, the laser beam corresponding to the magenta component is irradiated onto the surface of the second photoreceptor drum 11M from the left on the page to form an electrostatic latent image corresponding to the magenta component. The cyan component laser light is applied to the surface of the third photoreceptor drum 11C from the left in the drawing to form an electrostatic latent image of the cyan component. The black component laser light is applied to the surface of the fourth photoreceptor drum 11BK from the left in the drawing to form an electrostatic latent image of the black component.

After that, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of the respective colors are formed reach positions facing the developing section 13, respectively. Then, toner of each color is supplied from each developing section 13 to the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK, and the latent images formed on the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK are developed. (This is the developing process).
After that, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the development process reach the portions facing the intermediate transfer belt 17, respectively. Here, primary transfer rollers 14 are installed so as to come into contact with the inner peripheral surface of the intermediate transfer belt 17 at the respective opposing portions. Then, at the position of the primary transfer roller 14, the toner images of each color formed on the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK are sequentially superimposed and transferred onto the intermediate transfer belt 17 (primary transfer roller 14). process).

After the transfer process, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK reach positions facing the cleaning section 15, respectively. Then, the cleaning section 15 collects the untransferred toner remaining on the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK (this is a cleaning step).
After that, the surfaces of the photoreceptor drums 11Y, 11M, 11C, and 11BK pass through the static elimination unit, and a series of image forming processes on the photoreceptor drums 11Y, 11M, 11C, and 11BK are completed.

On the other hand, the intermediate transfer belt 17, on which the toners of the respective colors on the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK are superimposed and transferred (carried), travels clockwise in FIG. Reach the opposite position. Then, the color toner image carried on the intermediate transfer belt 17 is transferred onto the sheet P at a position facing the secondary transfer roller 18 (secondary transfer step).
After that, the surface of the intermediate transfer belt 17 reaches the position of the intermediate transfer belt cleaning section 16 . Then, the untransferred toner adhering to the intermediate transfer belt 17 is collected by the intermediate transfer belt cleaning section 16, and a series of transfer processes on the intermediate transfer belt 17 are completed.

Here, the sheet P conveyed between the intermediate transfer belt 17 and the secondary transfer roller 18 (secondary transfer nip) is conveyed from the paper supply unit 7 via the registration rollers 9 and the like. is.
Specifically, the sheet P fed from the sheet feeding unit 7 storing the sheet P by the sheet feeding roller 8 is guided to the registration rollers 9 after passing through the conveying path. The sheet P that has reached the registration rollers 9 is conveyed toward the secondary transfer nip in time.

Then, the sheet P onto which the full-color image has been transferred is guided to the fixing device 20 by the conveying belt. In the fixing device 20, a color image (toner image) is fixed on the surface of the sheet P at the nip portion (fixing nip) between the fixing roller and the pressure roller (fixing process).
After the fixing process, the sheet P is discharged as an output image to the outside of the apparatus main body 1 by a paper discharge roller, and a series of image forming processes (printing operation) is completed.

Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIGS. 2 and 3. FIG.
As shown in FIGS. 2 and 3, the fixing device 20 includes a fixing roller 21 as a fixing member, heaters 25 and 26 as heating means, a pressure roller 31 as a pressure member, and the temperature of the fixing roller 21 (surface temperature ), a moving mechanism 55 for moving the fixing roller 21 and the pressure roller 31 in the width direction, and the like.

Here, the fixing roller 21 (fixing rotator) as a fixing member is formed by laminating a coating layer 21b (an elastic layer and a release layer) on a core metal 21a having a hollow structure made of a metal material such as stainless steel. ) is formed, and is in pressure contact with a pressure roller 31 as a pressure member to form a nip portion (fixing nip).
The elastic layer of the covering layer 21b of the fixing roller 21 is made of an elastic material such as fluororubber, silicone rubber, or foamed silicone rubber. The release layer in the coating layer 21b of the fixing roller 21 is made of PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin) or the like. By providing the release layer on the surface layer of the fixing roller 21, the releasability (separability) of the toner T (toner image) is ensured. The fixing roller 21 is rotated clockwise in FIG. 2 by a drive motor (not shown).

Two heaters (a central heater 25 and an end heater 26) as heating means are fixed inside the fixing roller 21 (core metal 21a) having a hollow structure.
Each of the two heaters 25 and 26 is a bar-shaped halogen heater, and both ends thereof are fixed to side plates of the fixing device 20 . Electric power is supplied from the power sources 91 and 92 to the heaters 25 and 26 while the main switch of the image forming apparatus main body 1 is turned on (the power is turned on). Then, the fixing roller 21 is heated by radiant heat from the heaters 25 and 26 whose outputs are controlled by the control unit 90 , and heat is applied to the toner image T on the sheet P from the surface of the heated fixing roller 21 .
The output control of the heaters 25 and 26 is performed based on the detection result of the roller surface temperature by the two temperature sensors 40 and 41 facing the surface of the fixing roller 21 in a non-contact manner. By such output control of the heaters 25 and 26, the temperature (fixing temperature) of the fixing roller 21 can be adjusted and controlled to a desired temperature (target control temperature).
The two temperature sensors (center temperature sensor 40 and edge temperature sensor 41) will be described in more detail later.

The pressure roller 31 (pressure rotating body) as a pressure member is a roller member mainly composed of a metal core 32 and an elastic layer 33 as a coating layer covering the outer peripheral surface of the metal core 32 .
The elastic layer 33 (coating layer) of the pressure roller 31 is made of a material such as silicone rubber, foamed silicone rubber, or the like. A thin release layer made of PFA or the like may be provided on the surface of the elastic layer 33, and the elastic layer 33 and the release layer may form a covering layer.
The pressure roller 31 is pressed against the fixing roller 21 by a pressure mechanism (not shown). A desired nip portion is thus formed between the pressure roller 31 and the fixing roller 21 .
As the fixing roller 21 rotates, the pressure roller 31 rotates counterclockwise in FIG.
In this embodiment, the fixing roller 21 and the pressure roller 31 are configured to be movable in the width direction by the moving mechanism 55, which will be described later in detail.

The fixing device 20 configured as described above operates as follows.
When the main switch of the apparatus main body 1 is turned on, AC voltage is applied (powered) from the power sources 91 and 92 to the heaters 25 and 26 .
When a print command (print request) is input, a driving motor (driving mechanism) (not shown) starts to rotate the fixing roller 21 clockwise, and the pressure roller 31 is driven to rotate counterclockwise. be started. After that, the sheet P is fed from the paper feeding unit 7 , and the toner image on the intermediate transfer belt 17 is carried on the sheet P as an unfixed image at the position of the secondary transfer roller 18 . A sheet P carrying an unfixed image T (toner image) is conveyed in the direction of the arrow in FIG. Then, the toner image T is fixed on the surface of the sheet P by the heating by the fixing roller 21 and the pressing force of the fixing roller 21 and the pressure roller 31 . After the fixing process, the sheet P is fed in the direction of the arrow from the nip portion by the rotating fixing roller 21 and pressure roller 31 .

Hereinafter, the characteristic configuration and operation of the fixing device 20 (image forming apparatus 1) according to the present embodiment will be described in detail.
2 and 3, fixing device 20 in the present embodiment includes two heaters (central heater 25 and end heater 26) as heating means for heating fixing roller 21 (fixing member). ) is provided. As will be described later, the positions of the two heaters 25 and 26 in the width direction do not change even if the fixing roller 21 and the pressure roller 31 move in the width direction (the absolute positions in the width direction are fixed). .).

More specifically, referring to FIG. 3, the center heater 25 is set to the maximum width direction range M of the sheet P of the maximum size (maximum width direction size) that can be conveyed. 3) is a halogen heater capable of heating the fixing roller 21 within a heating range. The central heater 25 has a widthwise length substantially equal to the widthwise length of the fixing roller 21, but the portion that functions as a heater (heater main portion) is formed only in the central portion. The wattage of the central heater 25 is set to 850 W (watts). In the central heater 25 , the timing of application of voltage supplied from the first power supply 91 is adjusted (on/off control) by the control of the first power supply 91 (see FIG. 2 ) by the control section 90 .
The end heaters 26 cover the entire widthwise end portions of the maximum widthwise range M, excluding the widthwise central portion N (a range slightly wider than the range M in FIG. 3 excluding the range N). is a halogen heater capable of heating the fixing roller 21 with a heating range of . The end heaters 26 are formed so that the length in the width direction is substantially equal to the length in the width direction of the fixing roller 21, but the portions that function as heaters (heater main portions) are formed only at both ends. Also, the wattage of the end heater 26 is set to 800 W (watts). The end heaters 26 are controlled by the control unit 90 of the second power supply 92 (see FIG. 2) to adjust the timing of application of the voltage supplied from the second power supply 92 (on/off control).

In the present embodiment, the range N of the "widthwise central portion" of the fixing roller 21 described above is a range including the widthwise central position X (see FIG. 3), and is the minimum size of paper that can be passed. It is a sheet passing area for the sheet P, that is, a portion that can be a sheet passing area for sheets P of all sizes that can be passed.
In addition, the range M in the range (M - N) of the "both ends in the width direction" of the fixing roller 21 includes the sheet passing area of the maximum size sheet P that can be passed, and is a slightly wider range than that. is set to
In the present embodiment, these ranges M and N and the central position X do not change even if the fixing roller 21 and the pressure roller 31 move in the width direction, as will be described later (FIG. 4A). ), see (B)).

Here, referring to FIG. 4 and the like, in fixing device 20 of the present embodiment, fixing roller 21 (fixing member) is moved in the width direction without moving central heater 25 and end heater 26 in the width direction. A moving mechanism 55 is provided to move the pressing roller 31 (pressing member) to the other side in the width direction or to the other side in the width direction while moving the pressing roller 31 to the other side in the width direction or to the other side in the width direction.
That is, the moving mechanism 55 moves the fixing roller 21 and the pressure roller 31 not to the same side in the width direction but to different sides. Specifically, as shown in FIG. 4B, when the fixing roller 21 moves to one widthwise end side (the left side in FIG. 4B), the pressure roller 31 moves to the other widthwise end side (the left side in FIG. 4B). It will move to the right side of B). On the other hand, when the fixing roller 21 moves to the other widthwise end side (right side in FIG. 4), the pressure roller 31 moves to the widthwise one end side (left side in FIG. 4).

Although not shown, the moving mechanism 55 includes, for example, first and second holding members that rotatably hold the fixing roller 21 and the pressure roller 31, respectively, and the first and second holding members. First and second rack gears formed to extend in the width direction, first and second pinion gears respectively meshing with the first and second rack gears, and forward and reverse forward and reverse rotation of the first and second pinion gears. First and second motors rotatable in both directions, and first and second guide rails for holding the first and second holding members movably in the width direction.

Further, in the present embodiment, as shown in FIG. 4A, the moving mechanism 55 moves at least the maximum size when the sheet P1 of the maximum size M (for example, A3 vertical size) is transported. The fixing roller 21 and the pressure roller 31 are moved so as to form a nip (fixing nip, indicated by broken lines) in the wide direction range M (in the state shown in FIG. 4A). be). In this embodiment, the positions in the width direction of the fixing roller 21 and the pressure roller 31 shown in FIG. 4A are set as the reference position (home position).
On the other hand, as shown in FIG. 4B, the moving mechanism 55 is a small-size conveying mechanism for conveying a sheet P2 (for example, A4 vertical size) having substantially the same size as the central portion N in the width direction. Sometimes, the fixing roller 21 and the fixing roller 21 are arranged so that a nip portion (a fixing nip area indicated by a broken line) is formed only in a width direction range (small size width direction range N) that is substantially the same as the width direction central portion. The pressure roller 31 is moved (the state shown in FIG. 4B). That is, the fixing roller 21 is moved in the direction of the white arrow (to the left in the figure) from the reference position shown in FIG. 4A, and the pressure roller 31 is moved in the direction of the white arrow (to the right in the figure). Then, when the transport of the small size is shifted to the transport of the maximum size, the moving mechanism 55 moves the fixing roller 21 and the pressure roller 31 in the directions opposite to the directions of the white arrows in FIG. 4B. .
In the present embodiment, the above-described "during small-size transport" is defined as a time when the sheet P2 of the smallest size that can be transported is transported.

As described above, since the fixing device 20 according to the present embodiment is provided with the central heater 25 and the end heaters 26, the two heaters 25 and 26 are used to convey the maximum width direction range M (general) when the maximum size is conveyed. The entire paper area) is heated, and when the small size is conveyed, only the central heater 25 is used to heat the small size width direction range N (the entire paper passing area) so that the non-paper passing area is not actively heated. can be
Therefore, when a small-size sheet is conveyed, the problem of excessive temperature rise in the non-sheet-passing area (the widthwise portion of the fixing roller 21 where the nip portion is not formed) is less likely to occur.

Further supplementary description will be given.
If the heater for heating the fixing roller is formed so as to extend over the entire width direction, as in a conventional fixing device (see, for example, Patent Document 1), the fixing roller and the pressure roller can be used. When the widthwise length of the nipping portion is changed by moving it in the widthwise direction (when conveying a small size paper), the portion in the widthwise direction that forms the nipping portion of the fixing roller (paper passing area) by the single heater. At the same time, the widthwise portion (non-sheet-passing area) where the nip portion is not formed is also heated. As a result, there has been a problem that the widthwise portion of the fixing roller where the nip portion is not formed (non-sheet-passing region) is excessively heated. This is because the output of the heater is controlled based on the temperature detected by the temperature sensor in the paper-passing area, whereas in the non-paper-passing area heat is transferred from the fixing roller to the sheet unlike in the paper-passing area. because there is no If such an excessive temperature rise occurs, thermal damage or the like will occur at both ends of the fixing roller.
On the other hand, in the present embodiment, since the center heater 25 and the end heaters 26 are provided, it is possible to reduce the occurrence of such problems.

Information about the width direction sizes of the sheets P1 and P2 can be grasped by the control unit 90 based on the sheet information input by the user to the operation panel 100 (see FIGS. 1 and 2). Further, a size detection sensor is provided in the paper feeding unit 7 or the like, and the width direction size of the sheet P is directly detected by the size detection sensor, and information on the width direction size of the sheet P is acquired based on the detection result. You can also

Here, with reference to FIG. 4 and the like, fixing device 20 in the present embodiment is provided with two temperature sensors (center temperature sensor 40 and edge temperature sensor 41).
The center temperature sensor 40 is a temperature sensor capable of detecting the surface temperature of the fixing roller 21 both when conveying the maximum size and when conveying the small size. The central portion temperature sensor 40 is fixedly installed at a predetermined position (the central position X in the present embodiment) in the widthwise central portion N. As shown in FIG.
The edge temperature sensor 41 is a temperature sensor capable of detecting the surface temperature of the fixing roller 21 both when the maximum size is conveyed and when the small size is conveyed. there is Specifically, in this embodiment, since the fixing roller 21 moves to the left side (one end in the width direction) in FIG. An end temperature sensor 41 is fixed on the one end side).
In the present embodiment, non-contact temperature sensors (non-contact thermistors, thermopiles, etc.) are used as the temperature sensors 40 and 41 in order to avoid sliding contact due to the movement of the fixing roller 21. Contact-type temperature sensors can be used as the temperature sensors 40 and 41 when such problems due to sliding are unlikely to occur.

In the present embodiment, the center heater 25 is set so that the temperature detected by the center temperature sensor 40 reaches the target fixing temperature (for example, about 160° C.) regardless of whether the maximum size is conveyed or the small size is conveyed. On/off control is performed so that On the other hand, the edge heater 26 is controlled to turn on/off so that the temperature detected by the edge temperature sensor 41 becomes the fixing temperature (for example, about 160 degrees) when conveying the maximum size sheet. As a result, good fixed images are formed on the sheets P1 and P2 both when the maximum size is conveyed and when the small size is conveyed.
On the other hand, the edge heater 26 is controlled to turn on/off so that the temperature detected by the edge temperature sensor 41 becomes a predetermined temperature lower than the above-mentioned fixing temperature when conveying a small size sheet. Here, the predetermined temperature lower than the fixing temperature described above is set to the energy saving mode (in standby mode, power consumption is set to lower than that in printing, instead of completely shutting down power consumption, and the next printing operation is started. This is a control mode for quick operation.), for example, about 100 degrees. As a result, while suppressing excessive temperature rise at both ends of the fixing roller 21, it is possible to reduce the time required to raise the temperature of both ends of the fixing roller 21 to the target fixing temperature when the maximum size is conveyed again. .

In the present embodiment, the edge heater 26 is controlled to turn on/off so that the temperature detected by the edge temperature sensor 41 becomes a predetermined temperature lower than the fixing temperature when the small-size sheet is conveyed.
On the other hand, it is also possible to control so that the output of the edge heater 26 is turned off when conveying small-sized sheets. In that case, power consumption can be reduced.

<Modification 1>
As shown in FIG. 5, in the fixing device 20 according to Modification 1, when conveying a small size, the width direction portion of the fixing roller 21 (fixing member) where the nip portion is not formed and the pressure roller 31 (pressure member) A widthwise portion that does not form a nip portion is inserted into a duct 70 that generates an air flow inside the image forming apparatus main body 1 .
Specifically, referring to FIGS. 1 and 5 , the image forming apparatus main body 1 is provided with a duct 70 for exhausting the heat generated by the fixing device 20 to the outside of the image forming apparatus main body 1 . The duct 70 has an opening at one end connected to an exhaust fan 75 (installed in an opening that communicates with the inside and outside of the image forming apparatus main body 1 , see FIG. 1 ), and the other end directed toward the fixing device 20 . It is open. With such a configuration, heat generated in the fixing device 20 is sucked by the exhaust fan 75 through the duct 70 and exhausted to the outside of the image forming apparatus main body 1 . As a result, the problem that the ambient temperature inside the image forming apparatus main body 1 rises is alleviated.
5, the fixing roller 21 and the pressure roller 31 are moved in the width direction when the small size is conveyed, and the fixing roller 21 and the pressure roller 31 do not pass through the area. will be inserted into the duct 70 .
As a result, the non-paper-passing area between the fixing roller 21 and the pressure roller 31 is appropriately warmed by the exhaust heat (air having a relatively high temperature) flowing through the duct 70 .
Such a configuration is particularly useful when controlling the output of the end heater 26 to be turned off when conveying a small size. That is, even if the output of the end heater 26 is turned off when conveying a small size, excessive temperature rise at both ends of the fixing roller 21 is suppressed when conveying a small size, and when a transition is made from conveying a small size to conveying a maximum size. , the time required to raise the temperature of both ends of the fixing roller 21 to the target fixing temperature is shortened.

<Modification 2>
The fixing device 20 according to Modification 2 moves the fixing roller 21 toward one end in the width direction and moves the pressure roller 31 toward one end in the width direction, as shown in FIG. A first mode in which the fixing roller 21 is moved to the other side in the width direction, and a second mode in which the fixing roller 21 is moved to the other side in the width direction and the pressure roller 31 is moved to the one side in the width direction, as shown in FIG. 2 and , are both feasible.
That is, when the maximum size is conveyed, the fixing roller 21 and the pressure roller 31 are positioned in the width direction shown in FIG. 4(A). Then, when conveying a small size, the fixing roller 21 and the pressure roller 31 move to positions in the width direction shown in FIG. It will either move to a position (second form) or will. At the time of small-size transport, it is possible to control to alternately select whether to execute the first form or to execute the second form, or to select based on a predetermined condition. You can also
With this configuration, when conveying a small size, the end of the fixing roller 21 that is the non-paper-passing area is switched between one end and the other end, and the end that is the non-paper-passing area of the pressure roller 31 is switched. The part is switched between the one end side and the other end side. As a result, one end of the fixing roller 21 or the pressure roller 31 is locally worn and deteriorated compared to the other end due to repeated transition from the maximum size transport to the small size transport. will be mitigated.
In modification 2, a first end temperature sensor 41A detects the surface temperature of the fixing roller 21 when the fixing roller 21 moves to one end (left side) in the width direction as shown in FIG. 6A. In addition, as shown in FIG. 6B, a second end temperature sensor 41B is provided to detect the surface temperature of the fixing roller 21 when the fixing roller 21 moves to the other end (right side) in the width direction. is preferred.
The edge heater 26 is controlled to turn on/off so that the temperature detected by the edge temperature sensors 41A and 41B becomes the above-described fixing temperature (for example, about 160° C.) when the maximum size is conveyed. Further, the end heater 26 is turned on so that the temperature becomes lower than the fixing temperature based on the temperature detected by the first end temperature sensor 41A in the first form shown in FIG. It is turned off and controlled to be lower than the fixing temperature based on the temperature detected by the second edge temperature sensor 41B in the first mode shown in FIG. 6(B).
As a result, even if the length of the nip portion in the width direction is changed by moving the fixing roller 21 and the pressure roller 31 in the width direction, the width direction portion of the fixing roller 21 not forming the nip portion is excessively heated. It becomes difficult for troubles to occur.

<Modification 3>
As shown in FIG. 7, in the fixing device 20 according to Modification 3, the edge heater is smaller than the sheet P1 having the maximum size M and larger than the sheet P2 having the size substantially equal to the central portion N in the width direction. Alternatively, the width is changed so that the heating range of the fixing roller 21 can be varied according to the width direction size of a sheet of a plurality of width direction sizes (in the example of FIG. 7, one width direction size is medium size). A plurality of end heaters 26A and 26B are divided into a plurality of directional end portions.
Specifically, the main portion of the first end heater 26A is in a range (WN) obtained by subtracting the small size width direction range N from the width direction size of the medium size sheet (medium size width direction range W). are placed in The heater main portion of the second end heater 26B is arranged in a range (M−W) obtained by subtracting the middle size width direction range W from the maximum width direction range M. As shown in FIG. That is, these two end heaters 26A and 26B each heat a portion (only the divided portion) of the widthwise both ends of the maximum widthwise range M, excluding the widthwise central portion N, for fixing. It is configured to be able to heat the roller 21 .
Then, in Modification 3, the moving mechanism 55 moves the fixing roller 21 and the pressure roller 31 so that the nip portion is formed in accordance with the width direction size of the sheet P to be conveyed.
Specifically, as shown in FIG. 7A, when the maximum size sheet P (for example, a sheet of A3 vertical size) is passed, the nip portion is formed in the maximum width direction range M. , the fixing roller 21 and the pressure roller 31 are moved. On the other hand, as shown in FIG. 7B, when a medium-sized sheet P (for example, a sheet of A4 vertical size) is passed, a nip portion is formed in the medium-sized width direction range W. The fixing roller 21 and the pressure roller 31 are moved so as to move. Further, as shown in FIG. 7C, when a small size sheet P (for example, a sheet of A5 vertical size) is passed, the nip portion is formed in the small size width direction range N. Then, the fixing roller 21 and the pressure roller 31 are moved.
In Modification 3, as the edge temperature sensor, as shown in FIG. 7, a first sensor capable of detecting the temperature of the edge of the middle size width direction range W corresponding to the divided width direction both ends is provided. An edge temperature sensor 41A is provided, and a second edge temperature sensor 41B capable of detecting the temperature of the edge of the maximum width direction range M is provided.
When the maximum size is conveyed as shown in FIG. 7A, the center heater 25 is controlled to be on/off based on the temperature detected by the center temperature sensor 40 so as to achieve the target fixing temperature. The first end heater 26A is controlled to turn on/off so that the target fixing temperature is reached based on the temperature detected by the sensor 41A, and the target fixing temperature is reached based on the temperature detected by the second end temperature sensor 41B. The second end heater 26B is controlled to be on/off as described above.
7(B), the center heater 25 is turned on/off so that the target fixing temperature is reached based on the temperature detected by the center temperature sensor 40, and the first edge temperature is reached. The first end heater 26A is controlled to turn on and off based on the temperature detected by the sensor 41A so as to achieve the target fixing temperature. Also, based on the temperature detected by the second edge temperature sensor 41B, the second edge heater 26B is on/off controlled so that the temperature is lower than the fixing temperature.
7C, the center heater 25 is controlled to turn on and off based on the temperature detected by the center temperature sensor 40 so as to achieve the target fixing temperature. Also, the first edge heater 26A is turned on/off so that the temperature is lower than the fixing temperature based on the temperature detected by the first edge temperature sensor 41A, and the second edge temperature sensor 41B detects the temperature. The second end heater 26B is on/off controlled based on the temperature so that the temperature is lower than the fixing temperature.
As a result, even if the length of the nip portion in the width direction is changed by moving the fixing roller 21 and the pressure roller 31 in the width direction, the width direction portion of the fixing roller 21 not forming the nip portion is excessively heated. It becomes difficult for troubles to occur.

As described above, the fixing device 20 in the present embodiment includes the fixing roller 21 (fixing member) that heats a toner image and fixes it on the surface of the sheet P, and the sheet P that is conveyed by being in pressure contact with the fixing roller 21 . The pressure roller 31 (pressure member) forming the nip portion where the fixing roller 21 is formed and the fixing roller 21 can be heated only in the width direction central portion of the maximum width direction range M of the sheet P1 of the maximum size that can be conveyed. and end heaters 26 capable of heating the fixing roller 21 with a heating range covering all (or part of) both widthwise end portions of the maximum widthwise range M excluding the widthwise central portion N. , is provided. Further, without moving the center heater 25 and the end heaters 26 in the width direction, the fixing roller 21 is moved to the width direction one end side or the width direction other end side, and the pressure roller 31 is moved to the width direction other end side. Alternatively, a moving mechanism 55 is provided for moving to one end in the width direction. Then, the moving mechanism 55 moves the fixing roller 21 and the pressure roller 31 so that the nip portion is formed at least in the maximum width direction range M when the maximum size sheet P1 is transported. When a small-size sheet P2 having a size substantially equal to the central portion N in the width direction is conveyed, the nip portion is formed only in a range in the width direction substantially equal to the central portion N in the width direction. The pressure roller 31 is moved.
As a result, even if the length of the nip portion in the width direction is changed by moving the fixing roller 21 and the pressure roller 31 in the width direction, the width direction portion of the fixing roller 21 not forming the nip portion is excessively heated. It becomes difficult for troubles to occur.

It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be appropriately modified within the scope of the technical idea of the present invention other than suggested in the present embodiment. be. Moreover, the number, position, shape, etc. of the constituent members are not limited to those of the present embodiment, and the number, position, shape, etc. can be set to be suitable for carrying out the present invention.

In the specification of the present application and the like, the "width direction" is defined as a direction perpendicular to the sheet conveying direction.
In this specification and the like, the term "sheet" is defined to include all sheet-like recording media such as coated paper, label paper, OHP sheets, and film sheets, in addition to paper.

1 image forming apparatus (image forming apparatus main body),
20 fixing device,
21 fixing roller (fixing member),
25 central heater (heating means),
26, 26A, 26B end heaters (heating means),
31 pressure roller (pressure member),
40 central temperature sensor (first temperature detection means),
41, 41A, 41B edge temperature sensor (second temperature detection means),
55 moving mechanism,
70 ducts,
M maximum width direction range,
N Small size width direction range W Medium size width direction range
P, P1, P2 Sheets (paper).

JP-A-2002-83666

Claims (10)

a fixing member that heats the toner image to fix it on the surface of the sheet;
a pressing member that forms a nip portion where the sheet is conveyed by being pressed against the fixing member;
a central heater capable of heating the fixing member with only a central portion in the width direction as a heating range with respect to the maximum width direction range of the sheet of the maximum size that can be conveyed;
an edge heater capable of heating the fixing member with all or part of both widthwise end portions excluding the widthwise central portion of the maximum widthwise range as a heating range;
Without moving the central heater and the end heaters in the width direction, the fixing member is moved to one width direction end side or the other width direction end side, and the pressure member is moved to the width direction other end side or width direction. a moving mechanism for moving to one end in the direction;
with
The moving mechanism is
moving the fixing member and the pressure member so that the nip portion is formed at least in the maximum width direction range when the sheet of the maximum size is conveyed, and
When a small-size sheet is conveyed in which a sheet having a size substantially equal to that of the central portion in the width direction is conveyed, the nip portion is formed only in a range in the width direction that is substantially the same as the central portion in the width direction. A fixing device characterized by moving a pressure member. 2. The fixing device according to claim 1, wherein the small-size sheet is conveyed when a sheet of a minimum size that can be conveyed is conveyed. a center temperature sensor fixedly installed at a predetermined position in the center in the width direction and capable of detecting the surface temperature of the fixing member both during the transport of the maximum size and during the transport of the small size;
an end temperature sensor fixedly installed at a predetermined position at both ends in the width direction and capable of detecting the surface temperature of the fixing member both when the maximum size is conveyed and when the small size is conveyed;
3. The fixing device according to claim 1, further comprising: The center heater is controlled to turn on/off so that the temperature detected by the center temperature sensor becomes a target fixing temperature both during the transport of the maximum size and during the transport of the small size,
The edge heater is controlled to turn on and off so that the temperature detected by the edge temperature sensor is the fixing temperature when the maximum size is conveyed, and the temperature detected by the edge temperature sensor is the fixing temperature when the small size is conveyed. 4. The fixing device according to claim 3, wherein the fixing device is controlled to be on/off so as to reach a predetermined temperature lower than the temperature. The center heater is controlled to turn on/off so that the temperature detected by the center temperature sensor becomes a target fixing temperature both during the transport of the maximum size and during the transport of the small size,
The edge heater is controlled to turn on/off so that the temperature detected by the edge temperature sensor is equal to the fixing temperature when the maximum size is conveyed, and the output is turned off when the small size is conveyed. Item 4. The fixing device according to item 3. a first mode in which the fixing member is moved to one end in the width direction and the pressure member is moved to the other end in the width direction when the transport of the maximum size is shifted to the transport of the small size; to the other end in the width direction, and a second mode in which the pressure member is moved to the one end in the width direction. The fixing device according to . When the small size is conveyed, the widthwise portion of the fixing member that does not form the nip portion and the widthwise portion of the pressing member that does not form the nip portion generate an air flow inside the main body of the image forming apparatus. 7. The fixing device according to any one of claims 1 to 6, wherein the fixing device is inserted into a duct that allows the fixing device to move. 8. The fixing device according to claim 7, wherein the duct is for exhausting heat generated in the fixing device to the outside of the image forming apparatus main body. The end heaters are smaller than the maximum size sheet and larger than the sheet of size substantially equal to the width direction central portion, and the fixing is performed according to the width direction size of one or a plurality of width direction size sheets. A plurality of end heaters in which both ends in the width direction are divided into a plurality so that the heating range of the member is variable,
Claims 1 to 8, wherein the moving mechanism moves the fixing member and the pressure member so that the nip portion is formed in accordance with the size of the sheet to be conveyed in the width direction. The fixing device according to any one of . An image forming apparatus comprising the fixing device according to any one of claims 1 to 9.

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