JP2007279671A - Fixer and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixer which has excellent fixing property, starts up fast, does not have a fall of fixing temperature after starting up, and has good replacement efficiency of components and no displacement of a fixing sleeve, and to provide an image forming apparatus. <P>SOLUTION: The fixing sleeve 20 and a fixation assist roller 21 are so constituted that the internal diameter of the fixing sleeve 20 is larger than the external diameter of the fixation assist roller 21 before the temperature of the fixing sleeve 20 rises up to a predetermined value and the internal diameter of the fixing sleeve 20 becomes smaller than the external diameter of the fixation assist roller 21 when the temperature of the fixing sleeve 20 already reaches the predetermined value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine thereof, and a fixing device installed therein, and more particularly to a fixing device and an image forming apparatus using an electromagnetic induction heating method. It is.

  2. Description of the Related Art Conventionally, in image forming apparatuses such as copiers and printers, a technique using an electromagnetic induction heating type fixing device is widely known for the purpose of reducing the start-up time of the apparatus and saving energy (for example, (See Patent Document 1).

  In Patent Document 1, etc., an electromagnetic induction heating type fixing device includes a fixing roller having a heat generating layer, a magnetic flux generating means (external heating means) facing the fixing roller, a pressure roller in pressure contact with the fixing roller, and the like. . The magnetic flux generating means is configured by a coil portion (coil) or the like extending in the width direction (a direction orthogonal to the recording medium conveyance direction).

  The fixing roller (heat generation layer) is heated at a position facing the magnetic flux generation means. The heated fixing roller heats and fixes the toner image on the recording medium transported to the contact position (the fixing nip portion) with the pressure roller. Specifically, by passing a high-frequency alternating current through the coil portion, an alternating magnetic field is formed around the coil portion, and an eddy current is generated in the heat generating layer of the fixing roller. When an eddy current is generated in the heat generating layer, Joule heat is generated by the electric resistance of the heat generating layer. The entire fixing roller is heated by this Joule heat.

  On the other hand, Patent Document 2 and the like are electromagnetic induction heating type fixing devices, which include a fixing sleeve (metal sleeve) having a heat generating layer, a small-diameter fixing auxiliary roller (internal pressure member) inserted in the fixing sleeve, A magnetic flux generating means (induction heating source) facing the fixing sleeve, a pressure member (external pressure member) that presses the fixing auxiliary roller via the fixing sleeve, and the like are disclosed.

  The fixing sleeve (heat generation layer) is heated at a position facing the magnetic flux generation means. The heated fixing sleeve heats and fixes the toner image on the recording medium conveyed to a contact position (a fixing nip portion) with the pressure roller. Specifically, by passing a high-frequency alternating current through the coil portion, an alternating magnetic field is formed around the coil portion, and an eddy current is generated in the heat generation layer of the fixing sleeve. When an eddy current is generated in the heat generating layer, Joule heat is generated by the electric resistance of the heat generating layer. The entire fixing sleeve is heated by the Joule heat.

  These electromagnetic induction heating type fixing devices have high heat conversion efficiency compared to other types such as a heat roller type (heater lamp heating type) because the heat generating layer is directly heated by electromagnetic induction, It is known that the surface temperature (fixing temperature) of the fixing roller can be raised to a desired temperature with a small energy consumption and a short start-up time.

JP 2001-31168 A JP 10-740007 A

  The difference in configuration between the electromagnetic induction heating type fixing device in Patent Document 1 and the like described above and the electromagnetic induction heating type fixing device in Patent Document 2 or the like is that the heating layer (fixing sleeve) is integrated with the fixing auxiliary roller. It is whether or not. Specifically, in the former, the heat generating layer (fixing sleeve) is integrated with the heat insulating layer (fixing auxiliary roller) by adhesion with a primer or the like. On the other hand, in the latter, the inner diameter of the fixing sleeve is formed larger than the outer diameter of the auxiliary fixing roller, and the heat generating layer (fixing sleeve) is not integrated with the heat insulating layer (fixing auxiliary roller).

  There are mainly three problems with the former. The first problem is that since the deformation of the auxiliary fixing roller is limited by the fixing sleeve, a sufficient nip amount in the fixing nip portion cannot be secured and the fixing performance is deteriorated. The second problem is that since all of the inner peripheral surface of the fixing sleeve is in contact with the outer peripheral surface of the auxiliary fixing roller, the amount of heat conducted to the auxiliary fixing roller increases and the start-up of the apparatus is delayed. Is a point. The third problem is that since the fixing sleeve and the fixing auxiliary roller are integrated, it is necessary to replace both members at the same time even when only one of both members is damaged. That is the point.

  On the other hand, there are mainly two problems with the latter. The first problem is that since the contact area between the heat generating layer of the fixing sleeve and the heat insulating layer of the fixing auxiliary roller is small, it is difficult to store the heat of the heat generating layer after the apparatus starts up, and the fixing temperature drops. Is a point. The second problem is that since the fixing sleeve and the auxiliary fixing roller are not integrated, the fixing sleeve is displaced (moved in the axial direction) during operation of the apparatus.

  This invention has been made to solve the above-described problems, has good fixability, quick start-up of the apparatus, less drop in fixing temperature after start-up of the apparatus, and good component replacement efficiency. It is an object of the present invention to provide a fixing device and an image forming apparatus in which the fixing sleeve is not displaced.

  According to a first aspect of the present invention, a fixing device includes a magnetic flux generating means for generating a magnetic flux, a heat generating layer heated by the magnetic flux, and a fixing sleeve for fusing a toner image and fixing it on a recording medium. A fixing auxiliary roller inserted into the fixing sleeve, and the fixing sleeve and the fixing auxiliary roller have an inner diameter of the fixing sleeve when the temperature of the fixing sleeve is not raised to a predetermined value. It is formed so as to be larger than the outer diameter of the auxiliary roller, and is formed so that the inner diameter of the fixing sleeve becomes smaller than the outer diameter of the auxiliary fixing roller when the temperature of the fixing sleeve is raised to the predetermined value. It has been done.

  The fixing device according to a second aspect of the present invention is the fixing device according to the first aspect, wherein the predetermined value is higher than a target temperature for the fixing sleeve to melt and fix the toner image on the recording medium. It is small and larger than the ambient temperature.

  According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the fixing sleeve and the auxiliary fixing roller are configured such that the fixing sleeve and the auxiliary fixing roller are the first fixing sleeve when the start-up of the apparatus is started. The inner diameter of the fixing sleeve is larger than the outer diameter of the auxiliary fixing roller, and the inner diameter of the fixing sleeve is smaller than the outer diameter of the auxiliary fixing roller when the start-up of the apparatus is completed. It is.

  According to a fourth aspect of the present invention, in the fixing device according to any one of the first to third aspects, the fixing auxiliary roller is a regulating member that regulates the axial movement of the fixing sleeve. It is equipped with.

  A fixing device according to a fifth aspect of the present invention is the fixing device according to the fourth aspect, wherein the regulating member is a ring-shaped member inserted at both ends of the auxiliary fixing roller.

  The fixing device according to a sixth aspect of the present invention is the fixing device according to the fourth or fifth aspect, wherein the fixing sleeve has the restriction when the inner diameter thereof is larger than the outer diameter of the auxiliary fixing roller. By removing the member from the fixing auxiliary roller, the member can be extracted from the fixing auxiliary roller.

  A fixing device according to a seventh aspect of the present invention is the fixing device according to any one of the first to sixth aspects, wherein a lubricant is applied between the fixing sleeve and the auxiliary fixing roller. is there.

  According to an eighth aspect of the present invention, in the fixing device according to any one of the first to seventh aspects, the auxiliary fixing roller includes a heat insulating layer on an outer peripheral surface thereof.

  According to a ninth aspect of the present invention, in the fixing device according to the eighth aspect, the heat insulating layer is formed of an elastic material or an elastic foam material.

  According to a tenth aspect of the present invention, there is provided a fixing device according to any one of the first to ninth aspects, further comprising a pressure member that presses against the fixing auxiliary roller via the fixing sleeve. Is.

  According to an eleventh aspect of the present invention, in the fixing device according to any one of the first to tenth aspects, the magnetic flux generation means faces the fixing sleeve while an alternating current is input. A coil portion is provided.

  A fixing device according to a twelfth aspect of the present invention is a fixing device including a heated fixing sleeve, and includes a heat insulating roller having a non-contact region between the fixing sleeve and the heat insulating sleeve when cold. The non-contact area of the roller comes into contact with the fixing sleeve as the heat insulating roller thermally expands.

  According to a thirteenth aspect of the present invention, in the fixing device according to the twelfth aspect of the present invention, the non-contact area of the heat insulating roller is fixed to the non-contact region when the heat insulating roller reaches a predetermined temperature or more during startup. It is in contact with the sleeve.

  An image forming apparatus according to a fourteenth aspect of the present invention includes the fixing device according to any one of the first to thirteenth aspects.

  In the present invention, when the temperature of the fixing sleeve is not increased to a predetermined value, the inner diameter of the fixing sleeve is larger than the outer diameter of the auxiliary fixing roller, and when the temperature of the fixing sleeve is increased to the predetermined value, The inner diameter of the fixing auxiliary roller is smaller than the outer diameter of the auxiliary fixing roller. As a result, the fixing device and the image forming apparatus have good fixing properties, the apparatus starts up quickly, the fixing temperature does not drop significantly after the apparatus starts up, the parts replacement efficiency is good, and the fixing sleeve does not deviate. Can be provided.

Embodiment.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, reference numeral 1 denotes an apparatus main body of a tandem color copier as an image forming apparatus, 2 a writing unit that emits laser light based on input image information, and 3 an original conveying unit that conveys an original D to an original reading unit 4. 4 is a document reading unit that reads image information of the document D, 7 is a paper feeding unit that accommodates a recording medium P such as transfer paper, 9 is a registration roller that adjusts the conveyance timing of the recording medium P, and 11Y, 11M, and 11C. , 11BK are photosensitive drums on which toner images of respective colors (yellow, magenta, cyan, and black) are formed, 12 is a charging unit that charges the photosensitive drums 11Y, 11M, 11C, and 11BK, and 13 is each photosensitive drum. A developing unit that develops electrostatic latent images formed on 11Y, 11M, 11C, and 11BK, and a toner image formed on each of the photosensitive drums 11Y, 11M, 11C, and 11BK Transfer bias roller for transferring superimposed on the recording medium P, 15 denotes each of the photosensitive drums 11Y, 11M, 11C, cleaning unit for collecting the untransferred toner on 11BK, a.

  Reference numeral 16 denotes a transfer belt cleaning unit that cleans the transfer belt 17, reference numeral 17 denotes a transfer belt that conveys the recording medium P so that toner images of a plurality of colors are carried on the recording medium P, and reference numeral 19 denotes the recording medium P. 1 shows an electromagnetic induction heating type fixing device that fixes a toner image (unfixed image) of the toner.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport rollers of the document transport unit 3 and placed on the contact glass 5 of the document reading unit 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 light emitted from an illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each color separation light of RGB (red, green, blue) by the color sensor, and then converted into an electrical image signal. Further, color conversion processing, color correction processing, spatial frequency correction processing, and the like are performed by the image processing unit based on the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information.

  Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. The writing unit 2 emits laser light (exposure light) based on the image information of each color toward the corresponding photosensitive drums 11Y, 11M, 11C, and 11BK.

On the other hand, the four photosensitive drums 11Y, 11M, 11C, and 11BK are rotated clockwise in FIG. First, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11BK are uniformly charged at a portion facing the charging unit 12 (this is a charging process). Thus, a charged potential is formed on the photosensitive drums 11Y, 11M, 11C, and 11BK. Thereafter, the charged surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK reach the irradiation positions of the respective laser beams.
In the writing unit 2, laser light corresponding to the image signal is emitted from the four light sources corresponding to each color. Each laser beam passes through a separate optical path for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  Laser light corresponding to the yellow component is irradiated on 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) of the photosensitive drum 11Y by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11Y charged by the charging unit 12.

  Similarly, the laser beam corresponding to the magenta component is irradiated onto the surface of the second photosensitive drum 11M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser light is applied to the surface of the third photosensitive drum 11C from the left side of the paper, and an electrostatic latent image of the cyan component is formed. The black component laser beam is applied to the surface of the fourth photosensitive drum 11BK from the left side of the paper, and an electrostatic latent image of the black component is formed.

Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK on which the electrostatic latent images of the respective colors are formed reach positions facing the developing unit 13, respectively. Then, the respective color toners are supplied from the developing units 13 to the photosensitive drums 11Y, 11M, 11C, and 11BK, and the latent images on the photosensitive drums 11Y, 11M, 11C, and 11BK are developed (developing process). .)
Thereafter, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the development process reach the facing portions of the transfer belt 17, respectively. Here, a transfer bias roller 14 is installed at each facing portion so as to contact the inner peripheral surface of the transfer belt 17. Then, the toner images of the respective colors formed on the photoconductive drums 11Y, 11M, 11C, and 11BK are sequentially superimposed and transferred onto the recording medium P on the transfer belt 17 at the position of the transfer bias roller 14 (transfer process). .)

Then, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11BK after the transfer process reach positions facing the cleaning unit 15, respectively. Then, the untransferred toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11BK is collected by the cleaning unit 15 (this is a cleaning process).
Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11BK pass through a neutralization unit (not shown), and a series of image forming processes on the photoconductive drums 11Y, 11M, 11C, and 11BK is completed.

On the other hand, the recording medium P on which the toners of the respective colors on the photosensitive drums 11Y, 11M, 11C, and 11BK are transferred (carrying) is run in the direction of the arrow in the drawing and reaches a position facing the separation charger 18. . Then, the charge accumulated in the recording medium P is neutralized at a position facing the separation charger 18, and the recording medium P is separated from the transfer belt 17 without causing toner dust or the like.
Thereafter, the surface of the transfer belt 17 reaches the position of the transfer belt cleaning unit 16. Then, the deposit adhered on the transfer belt 17 is collected by the transfer belt cleaning unit 16.

Here, the recording medium P transported onto the transfer belt 17 is transported from the paper feeding unit 7 via the registration rollers 9 and the like.
Specifically, the recording medium P fed by the paper feeding roller 8 from the paper feeding unit 7 that stores the recording medium P passes through a conveyance guide (not shown) and is guided to the registration roller 9. The recording medium P that has reached the registration roller 9 is conveyed toward the position of the transfer belt 17 in time.

The recording medium P to which the full color image has been transferred is separated from the transfer belt 17 and then guided to the fixing device 19. In the fixing device 19, the color image (toner) is fixed on the recording medium P at the nip between the fixing sleeve and the pressure roller.
Then, the recording medium P after the fixing step is discharged as an output image outside the apparatus main body 1 by a discharge roller (not shown), and a series of image forming processes is completed.

Next, the configuration and operation of the fixing device 19 installed in the image forming apparatus main body 1 will be described in detail.
As shown in FIG. 2, the fixing device 19 includes an induction heating unit 24 as a magnetic flux generating unit, a fixing sleeve 20, a fixing auxiliary roller 21 (heat insulating roller), a pressure roller 30 as a pressure member, and the like. .

Here, the fixing sleeve 20 is a multilayer structure in which an elastic layer, a release layer, and the like are formed on the surface of a heat generating layer formed of a magnetic metal material such as iron, cobalt, nickel, or an alloy thereof.
The heat generation layer of the fixing sleeve 20 has a layer thickness of 30 to 100 μm, and is heated by electromagnetic induction by a magnetic flux emitted from the induction heating unit 24 (magnetic flux generating means). In addition to the magnetic metal material described above, a nonmagnetic metal material such as SUS304 or SUS316 can be used as the material for the heat generating layer, and a good conductor such as copper or aluminum is 5 to 20 μm thick on polyimide resin or the like. Those plated with can also be used. Furthermore, the heat generating layer may have a two-layer structure of a first nonmagnetic layer and a second nonmagnetic layer having different volume resistivity.

The elastic layer of the fixing sleeve 20 has a layer thickness of 30 to 200 μm and is formed of silicone rubber or the like. By providing the fixing sleeve 20 with an elastic layer, it is possible to suppress the occurrence of uneven fixing particularly in a color image forming apparatus.
The release layer of the fixing sleeve 20 has a layer thickness of 20 to 50 μm and is made of a fluorine compound such as PFA. The release layer is for improving the toner release property on the surface of the fixing sleeve 20 with which the toner image (toner) T is in direct contact.

The fixing auxiliary roller 21 as a heat insulating roller is formed by forming a heat insulating layer 22 having heat resistance on a metal core 23 made of stainless steel.
The heat insulating layer 22 of the auxiliary fixing roller 21 has a layer thickness of 2 to 5 mm and an Asker hardness of 20 to 50 degrees. As a material of the heat insulation layer 22, an elastic material such as silicone rubber or an elastic foam material such as foamed silicone rubber can be used.

  Here, the fixing auxiliary roller 21 is inserted into the fixing sleeve 20, but the fixing auxiliary roller 21 and the fixing sleeve 20 are not bonded (integrated). When the temperature of the fixing sleeve 20 is not raised to a predetermined value, the inner diameter of the fixing sleeve 20 is larger than the outer diameter of the auxiliary fixing roller 21 (the state shown in FIG. 3), and the temperature of the fixing sleeve 20 is increased. The fixing sleeve 20 and the auxiliary fixing roller 21 are configured so that the inner diameter of the fixing sleeve 20 is smaller than the outer diameter of the auxiliary fixing roller 21 when the temperature is raised to a predetermined value (the state shown in FIG. 2). (The material and shape are adjusted.) This will be described in detail later.

  Although not shown, a thermistor is in contact with the surface of the fixing sleeve 20. The thermistor is a temperature sensitive element with high thermal responsiveness, and detects the temperature on the fixing sleeve 20 (fixing temperature). Then, the heating amount by the induction heating unit 24 is adjusted based on the detection result by the thermistor.

  Here, referring to FIG. 4, ring-shaped members 40 are inserted at both ends of the auxiliary fixing roller 21 as a restricting member for restricting the axial movement of the fixing sleeve covering the outer peripheral surface thereof. Specifically, a ring-shaped member 40 is inserted into the shaft portion 21 a of the auxiliary fixing roller 21 on which the fixing sleeve 20 is installed, and a retaining ring 45 is inserted outside the ring-shaped member 40. Since the outer diameter of the ring-shaped member 40 is larger than the outer diameter of the auxiliary fixing roller 21, even if the fixing sleeve 20 tries to move in the axial direction (thrust direction), the ring-shaped member 40 abuts on the ring-shaped member 40 and its operation is restricted. . Thus, even when the inner diameter of the fixing sleeve 20 is larger than the outer diameter of the auxiliary fixing roller 21, the deviation of the fixing sleeve 20 is limited.

  When the inner diameter of the fixing sleeve 20 is larger than the outer diameter of the auxiliary fixing roller 21, the fixing sleeve 20 can be easily extracted from the auxiliary fixing roller 21 by taking out the ring-shaped member 40 from the auxiliary fixing roller 21. Can do. Thereby, the replacement efficiency of the parts of the fixing sleeve 20 and the auxiliary fixing roller 21 is improved.

  In this embodiment, grease as a lubricant is applied between the fixing sleeve 20 and the auxiliary fixing roller 21. As a result, the frictional resistance between the fixing sleeve 20 and the auxiliary fixing roller 21 is reduced, the axial displacement of the fixing sleeve 20 is reduced, and the attaching / detaching operation of the fixing sleeve 20 with respect to the auxiliary fixing roller 21 is simplified. .

  Referring to FIG. 2, a pressure roller 30 as a pressure member has an elastic layer 31 made of silicone rubber or the like and a release layer made of PFA or the like formed on a cylindrical member 32 made of aluminum, copper or the like. Is. The elastic layer 31 of the pressure roller 30 is formed to have a thickness of 1 to 5 mm. The release layer of the pressure roller 30 is formed so that the layer thickness is 20 to 50 μm. The pressure roller 30 is in pressure contact with the auxiliary fixing roller 21 via the fixing sleeve 20. Then, the recording medium P is conveyed to a contact portion (a fixing nip portion) between the fixing sleeve 20 and the pressure roller 30.

The induction heating unit 24 as a magnetic flux generating means includes a coil unit 25 (excitation coil), a core unit 26 (excitation coil core), a coil guide 27, a cover member 28, and the like. The coil portion 25 is wound in the width direction (in the direction perpendicular to the paper surface of FIG. 2) by winding a litz wire bundled with thin wires on a coil guide 27 disposed so as to cover a part of the outer peripheral surface of the fixing sleeve 20. It is extended. The coil guide 27 is made of a heat-resistant resin material or the like, and holds the coil portion 25 on the side facing the fixing sleeve 20. The core portion 26 is made of a ferromagnetic material such as ferrite (relative magnetic permeability is about 2500), and a center core and a side core are provided in order to form an efficient magnetic flux toward the heat generating layer of the fixing sleeve 20. ing. The core part 26 is installed so as to face the coil part 25 extending in the width direction. The cover member 28 is configured to cover the coil portion 25, the core portion 26, and the coil guide 27.
An internal core (core) made of a ferromagnetic material such as ferrite can be installed inside the auxiliary fixing roller 21, or a magnetic flux shielding member that covers a part of the outer periphery of the internal core can also be installed.

The fixing device 19 configured as described above operates as follows.
When the auxiliary fixing roller 21 is driven to rotate in the clockwise direction in FIG. 2 by a drive motor (not shown), the fixing sleeve 20 also rotates in the clockwise direction following the rotation, and the pressure roller 30 rotates in the counterclockwise direction. Rotate. The fixing sleeve 20 is heated by a magnetic flux generated from the induction heating unit 24 at a position facing the induction heating unit 24 (opposed surface).

  Specifically, by applying a high-frequency alternating current of 10 kHz to 1 MHz (preferably 20 kHz to 800 kHz) from the power supply unit (not shown) to the coil unit 25, the magnetic field lines from the coil unit 25 toward the heat generating layer of the fixing sleeve 20. Are alternately switched in both directions. By forming the alternating magnetic field in this way, an eddy current is generated in the heat generating layer of the fixing sleeve 20, and the heat generating layer generates Joule heat due to its electric resistance and is induction heated. Thus, the fixing sleeve 20 is heated by induction heating of its own heat generation layer.

Thereafter, the surface of the fixing sleeve 20 heated by the induction heating unit 24 reaches a contact portion with the pressure roller 30. Then, the toner image T (toner) on the conveyed recording medium P is heated and melted.
Specifically, the recording medium P carrying the toner image T through the image forming process described above is fed between the fixing sleeve 20 and the pressure roller 30 while being guided by a guide plate (not shown) (arrow). Y1 movement in the transport direction.) The toner image T is fixed to the recording medium P by the heat received from the fixing sleeve 20 and the pressure received from the pressure roller 30, and the recording medium P is sent out between the fixing sleeve 20 and the pressure roller 30.

The surface of the fixing sleeve 20 that has passed the fixing position then reaches the position facing the induction heating unit 24 again.
Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

Hereinafter, the configuration and operation of the fixing device 19 characteristic of the present embodiment will be described.
FIG. 5 is a graph showing changes in the inner diameter of the fixing sleeve 20 and changes in the outer diameter of the auxiliary fixing roller 21 with respect to temperature changes. In FIG. 5, the horizontal axis indicates the temperature (the temperature of the fixing sleeve 20), and the vertical axis indicates the inner diameter of the fixing sleeve 20 or the outer diameter of the auxiliary fixing roller 21. A solid line R1 indicates a temperature change of the inner diameter of the fixing sleeve 20, and a solid line R2 indicates a temperature change of the outer diameter of the auxiliary fixing roller 21.

  As shown in FIG. 5, in the present embodiment, when the temperature of the fixing sleeve 20 is not raised to a predetermined value (about 100 ° C. in the present embodiment) (when cold), the fixing sleeve 20 is used. The inner diameter of 20 is set to be larger than the outer diameter of the auxiliary fixing roller 21 (the state shown in FIG. 3). Therefore, when the start-up of the fixing device 19 is started, the inner diameter of the fixing sleeve 20 is larger than the outer diameter of the auxiliary fixing roller 21. Specifically, at normal temperature, the inner diameter of the fixing sleeve 20 is 40 mm, and the outer diameter of the auxiliary fixing roller 21 is 39.5 mm. In FIG. 5, the temperature at the start of startup varies depending on the use environment (atmosphere temperature).

  Further, when the temperature of the fixing sleeve 20 is raised to a predetermined value (about 100 ° C. in the present embodiment), the inner diameter of the fixing sleeve 20 is made smaller than the outer diameter of the auxiliary fixing roller 21. (The state shown in FIG. 2). Therefore, at least when the start-up of the fixing device 19 is completed, the inner diameter of the fixing sleeve 20 becomes smaller than the outer diameter of the auxiliary fixing roller 21. Specifically, when the paper is passed (during the fixing process), the inner diameter of the fixing sleeve 20 is 40 to 40.1 mm, and the outer diameter of the auxiliary fixing roller 21 is 40.4 to 40.7 mm.

  Here, the predetermined value (the temperature at which the relationship between the inner diameter of the fixing sleeve 20 and the outer diameter of the auxiliary fixing roller 21 is reversed) is fused by the fixing sleeve 20 and fixed on the recording medium P. Therefore, the temperature is lower than the target temperature (around 160 ° C.) and higher than the ambient temperature.

  With such a configuration, for a while after the start-up (warming-up) of the fixing device 19 is started, the induction heating unit is in a state where there is a gap (non-contact area) between the fixing sleeve 20 and the auxiliary fixing roller 21. The fixing sleeve 20 (heat generation layer) is heated by 24. Therefore, the heat transfer from the fixing sleeve 20 to the fixing auxiliary roller 21 is reduced, and the start-up time is shortened.

This can be understood from the experimental results shown in FIG. In FIG. 6, a solid line S1 indicates a rising characteristic (temperature rise characteristic of the fixing sleeve 20) when the fixing sleeve 20 and the auxiliary fixing roller 21 are not integrated (adhered) and there is a gap between them, and a solid line S2 indicates the fixing sleeve. 20 shows the rising characteristics when the fixing auxiliary roller 21 is integrated (adhered) 20 and there is no gap between the two.
As shown in FIG. 6, the start-up time when there is no gap between the fixing sleeve 20 and the fixing auxiliary roller 21 is about 24 seconds, whereas between the fixing sleeve 20 and the fixing auxiliary roller 21. The start-up time when there is a gap is about 17 seconds.

That is, according to the present embodiment, since the gap is provided between the fixing sleeve 20 and the auxiliary fixing roller 21 at the time of startup, the startup time of the fixing device 19 is surely shortened.
In addition, since the fixing sleeve 20 and the fixing auxiliary roller 21 are not integrated, a problem that deformation of the fixing auxiliary roller 21 is limited by the fixing sleeve 20 is reduced, and a sufficient nip amount of the fixing nip portion is secured. Can be improved.
Further, since there is a gap between the fixing sleeve 20 and the auxiliary fixing roller 21 at normal temperature (maintenance), even when only one of the two members is damaged or the like, both members are simultaneously attached. There is no need to replace it. As described above with reference to FIG. 4, the disassembly work of the fixing sleeve 20 and the auxiliary fixing roller 21 can be easily performed.

On the other hand, when the fixing device 19 has been started up (warming up) and the fixing step (paper passing) is performed, there is no gap between the fixing sleeve 20 and the auxiliary fixing roller 21 (the contact area between both members is In this state, the fixing sleeve 20 (heat generation layer) is heated by the induction heating unit 24. Therefore, the heat generated in the fixing sleeve 20 is stored in the heat insulating layer 22 of the auxiliary fixing roller 21, and the decrease in fixing temperature immediately after the fixing process (when moving to the next fixing process) is reduced.
In this embodiment, since the heat insulating layer 22 of the auxiliary fixing roller 21 is formed of an elastic material (or elastic foam material), the outer diameter of the auxiliary fixing roller 21 is larger than the inner diameter of the fixing sleeve 20. However, no great stress is generated on the fixing sleeve 20.

  In addition, since there is no gap between the fixing sleeve 20 and the auxiliary fixing roller 21 during the fixing process (when paper is passed) (because both members are in close contact), the fixing sleeve is in operation during the operation of the fixing device. A problem that a shift of 20 (movement in the axial direction) occurs is suppressed. In the present embodiment, as described above with reference to FIG. 4, since the ring-shaped member 40 as the regulating member is installed on the fixing auxiliary roller 21, the occurrence of the deviation of the fixing sleeve 20 is reliably suppressed. Will be.

In other words, the fixing device in this embodiment has the following characteristic configuration.
That is, the fixing device in the present embodiment includes a heat insulating roller (fixing auxiliary roller) 21 having a non-contact area (air layer) between the fixing sleeve 20 and the fixing sleeve 20 when cold. 21 is brought into contact with the fixing sleeve 20 by thermal expansion. Specifically, when the heat insulating roller 21 reaches a predetermined temperature or higher when the apparatus is started up (warming up), the non-contact area of the heat insulating roller 21 contacts the fixing sleeve 20.

  As described above, in the present embodiment, when the temperature of the fixing sleeve 20 is not raised to a predetermined value, the inner diameter of the fixing sleeve 20 is larger than the outer diameter of the auxiliary fixing roller 21, and the temperature of the fixing sleeve 20 is increased. Is configured so that the inner diameter of the fixing sleeve 20 is smaller than the outer diameter of the auxiliary fixing roller 21 when the temperature is increased to a predetermined value. As a result, the fixing property is good, the fixing device 19 starts up quickly, the fixing temperature drops little after the fixing device 19 starts up, the parts (the fixing sleeve 20 and the auxiliary fixing roller 21) are exchanged efficiently, and the fixing sleeve The shift of 20 can be reduced.

  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 modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 4 is a cross-sectional view illustrating a state when the fixing device is passing paper. FIG. 3 is a cross-sectional view illustrating a state at the start of starting up the fixing device. It is a perspective view which shows a fixing auxiliary roller. 5 is a graph showing a change in inner diameter of a fixing sleeve and a change in outer diameter of a fixing auxiliary roller with respect to a temperature change. 5 is a graph showing a difference in rising characteristics when the fixing sleeve and the fixing auxiliary roller are integrated and when they are not integrated.

Explanation of symbols

1 image forming apparatus body (apparatus body),
19 fixing device,
20 fixing sleeve,
21 fixing auxiliary roller (heat insulating roller), 22 heat insulating layer, 23 cored bar,
24 induction heating part (magnetic flux generating means),
25 coil section, 26 core section,
27 Coil guide, 28 Cover member,
30 pressure roller,
40 Ring-shaped member (regulating member).

Claims (14)

Magnetic flux generating means for generating magnetic flux;
A fixing sleeve that has a heat generating layer heated by the magnetic flux and that melts and fixes the toner image to a recording medium;
A fixing auxiliary roller inserted in the fixing sleeve,
The fixing sleeve and the auxiliary fixing roller are formed such that an inner diameter of the fixing sleeve is larger than an outer diameter of the auxiliary fixing roller when the temperature of the fixing sleeve is not raised to a predetermined value. The fixing device is characterized in that an inner diameter of the fixing sleeve is smaller than an outer diameter of the auxiliary fixing roller when the temperature of the fixing sleeve is raised to the predetermined value.   2. The fixing device according to claim 1, wherein the predetermined value is smaller than a target temperature for the fixing sleeve to melt and fix the toner image on the recording medium and larger than an ambient temperature.   The fixing sleeve and the fixing auxiliary roller are formed so that the inner diameter of the fixing sleeve is larger than the outer diameter of the fixing auxiliary roller when the apparatus starts up, and when the apparatus starts up, The fixing device according to claim 1, wherein an inner diameter of the fixing sleeve is formed to be smaller than an outer diameter of the auxiliary fixing roller.   The fixing device according to claim 1, wherein the fixing auxiliary roller includes a regulating member that regulates movement of the fixing sleeve in an axial direction.   The fixing device according to claim 4, wherein the restricting member is a ring-shaped member inserted at both ends of the fixing auxiliary roller.   The fixing sleeve is configured to be able to be taken out from the auxiliary fixing roller by taking out the regulating member from the auxiliary fixing roller when the inner diameter thereof is larger than the outer diameter of the auxiliary fixing roller. The fixing device according to claim 4 or 5.   The fixing device according to claim 1, wherein a lubricant is applied between the fixing sleeve and the auxiliary fixing roller.   The fixing device according to claim 1, wherein the fixing auxiliary roller includes a heat insulating layer on an outer peripheral surface thereof.   The fixing device according to claim 8, wherein the heat insulating layer is formed of an elastic material or an elastic foam material.   The fixing device according to claim 1, further comprising a pressing member that presses against the fixing auxiliary roller via the fixing sleeve.   The fixing device according to claim 1, wherein the magnetic flux generation unit includes a coil portion that receives an alternating current and faces the fixing sleeve. In a fixing device comprising a heated fixing sleeve,
A heat insulating roller having a non-contact area with the fixing sleeve when cold;
The fixing device according to claim 1, wherein the non-contact region of the heat insulating roller contacts the fixing sleeve as the heat insulating roller thermally expands.   The fixing device according to claim 12, wherein the non-contact region of the heat insulating roller comes into contact with the fixing sleeve when the heat insulating roller reaches a predetermined temperature or more during startup.   An image forming apparatus comprising the fixing device according to claim 1.

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