JP2011123182A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device configured to stabilize the rotating path of a fixing belt even when eliminating the need for a fixing plate used for regulating the distance between the fixing belt and an induction coil. <P>SOLUTION: The fixing device secures a fixing nip N by pressing a fixing roller 150 inserted inside the fixing belt 154 with play by a pressure roller 160, performs induction heating of the fixing belt 154 by means of the induction coil 171 while rotating the fixing belt 154, and passes a sheet with an unfixed image formed thereon through the fixing nip N to perform heat fixing. In the fixing device, a pair of regulating members for the fixing belt 154 are disposed at both axial ends of the fixing roller 150 in an axial direction, the regulating members having rings 157a and being configured to regulate the outside diameter of the fixing belt 154 by the contact of the peripheries of both edges of the fixing belt 154 with the internal surfaces of the rings 157a. When the fixing belt 154 is heated and is not pressed by the pressure roller 160, the difference between the inside diameter of the ring 157 and the outside diameter of each of the edges of the fixing belt 154 is equal to or smaller than the maximum value of the sum of the tolerances of both the diameters. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus that heat-fix an unfixed image on a recording sheet by heating a fixing belt by induction heating, and particularly relates to a technique for improving the fixing quality.

In recent years, as a fixing device for an image forming apparatus such as a copying machine, an electromagnetic induction heating type fixing device capable of raising the temperature in a short time for power saving is becoming mainstream.
4A and 4B are diagrams illustrating an example of the configuration of a conventional electromagnetic induction heating type fixing device. 4A is a cross-sectional view including the roller shaft of the fixing device, and FIG. 4B is a cross-sectional view taken along a line PP ′ in FIG. 4A.

  As shown in both figures, this fixing device includes a fixing roller 1150 having an outer diameter smaller than the inner diameter of an endless fixing belt 1154 having an induction heat generating layer. A plate-shaped fixing plate 1155 that keeps the distance L0 between the magnetic flux generation unit 170 and the fixing belt 1154 constant is disposed between the roller 1150 and the position facing the magnetic flux generation unit 170.

An elastic layer 1152 is formed on the peripheral surface of the fixing roller 1150 excluding both ends of the cylindrical roller shaft 1151, and a fixing nip N is formed by pressure contact with the pressure roller 1160 from the outside of the fixing belt 1154 ( The fixing device in which the fixing roller is loosely inserted in the fixing belt in this manner is hereinafter referred to as a “loose fitting type fixing device”).
According to the loose-fitting type fixing device, since the fixing belt 1154 is not in close contact with the fixing roller 1150, the heat of the fixing belt 1154 is not easily taken by the fixing roller, and the temperature can be increased in a short time, thereby forming an image. There is an advantage that the time to start can be shortened.

However, in the configuration of the fixing device 1005 having the above-described configuration, since the contact area between the fixing belt 1154 and the fixing plate 1155 is large, the wear of the fixing belt 1154 is relatively large, and there is a problem in terms of durability. Has been.
Therefore, as shown by two-dot chain lines in FIGS. 4A and 4B, a pair of flange-shaped belt regulating members 1157 are provided at both ends of the fixing roller 1150, respectively. It is conceivable to employ a configuration in which only the outer periphery of both end portions of the fixing belt 1154 is brought into contact with the fixing belt 1154 so as to restrict the circulation path.

In addition, the flange shape said here means the shape which has a ring-shaped edge part on the outer periphery of the disk-shaped member which has a hole in the center.
4A shows only one end portion of the fixing device 1005, the other end portion has the same configuration.

JP 2007-279671 A

However, when the fixing device 1005 provided with the flange-shaped belt regulating member 1157 is actually driven, when the pressure roller is pushed in to form the fixing nip N, the circumferential end of the fixing nip N is caused by the rigidity of the fixing belt itself. As a result, the fixing belt 1154 is slightly deformed into an elliptical shape as shown in FIG. 4C.
For this reason, it is found that the belt regulating member 1157 cannot receive guidance at the portions of the fixing belt 1154 and the magnetic flux generator 170 that face each other, and the distance L1 fluctuates greatly, resulting in uneven heating and deterioration in fixing quality. did.

  The present invention has been made in view of the above problems, and uses a loose-fitting type fixing device capable of suppressing deterioration in fixing quality while ensuring the durability of the fixing belt, and the same. An object is to provide an image forming apparatus.

  In order to achieve the above object, a fixing device according to the present invention presses a first roller loosely inserted inside an endless belt with a second roller from the outer circumference of the belt through the belt. A fixing nip is secured between the belt surface and the second roller, and induction heating is performed by a high-frequency magnetic field generated by an induction coil while the belt is circulated, so that the sheet on which an unfixed image is formed is fixed. A fixing device for thermally fixing the unfixed image through a nip, wherein the first roller has a flange shape having ring-shaped edges at both ends in the axial direction, and the ring-shaped portion. A pair of belt regulating members for regulating the outer diameter of the belt are disposed on the inner surface of the belt, the outer circumferences of both ends of the belt being in contact with each other, the belt is heated to a predetermined temperature, and the first 2 b In a state in which pressing by La is not performed, the difference between the outer diameter of both ends of an inner diameter and said belt of said inner surface, characterized in that is less than or equal to the maximum value of the sum of the tolerances of both diameter.

With the above configuration, in the loose-fitting type fixing device, only the both end portions of the belt are brought into contact with the inner surface of the flange-shaped belt regulating member to regulate the circulation path, so that the area of the friction portion is fixed as in the conventional case. The belt becomes much smaller than when a plate is used, and the durability of the belt is improved.
In addition, the inner diameter of the belt regulating member and the outer diameter of the belt are determined so that the outer circumferences of both ends of the belt can be brought into contact with the inner surface of the belt regulating member without any gap even if the nip portion is formed. The belt circulation path is stabilized, the positional relationship between the electromagnetic induction generator and the belt is less changed, and heating unevenness is eliminated to improve the fixing quality.

Further, during execution of the fixing operation, the first distance is set such that the radial distance between the outer peripheral surface of the belt and the inner surface located outside the fixing nip formation range is within a range of 0.7 mm or less. It is desirable that the outer diameter of the roller be determined.
Thereby, since the fluctuation | variation of the circumference path of a belt is restrict | limited more, the circumference path of a belt can be stabilized more and it contributes to the improvement of fixing quality.

  Note that the present invention may be an image forming apparatus including the fixing device.

1 is a schematic cross-sectional view illustrating an overall configuration of a printer according to an embodiment of the present invention. FIG. 2 is a partially cutaway perspective view showing a configuration of a fixing device according to an embodiment of the present invention. (A), (b), (c) is principal part sectional drawing in the said fixing device. (A), (b), (c) is principal part sectional drawing in the conventional fixing device.

Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of a tandem type full-color printer according to the present embodiment.
As shown in the figure, the printer 1 includes an image processing unit 3, a paper feeding unit 4, a fixing unit 5, and a control unit 60. The printer 1 is connected to a network (for example, a LAN) and is connected to an external terminal device (not connected). When a print job execution instruction is received from (shown), a toner image composed of yellow, magenta, cyan, and black is formed based on the instruction, and a full-color image is formed by multiple transfer of these. Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are represented as Y, M, C, and K, and Y, M, C, and K are added as subscripts to the numbers of the components related to the reproduction colors.

<Image process part>
The image processing unit 3 includes image forming units 3Y, 3M, 3C, and 3K corresponding to each of Y to K colors, an optical unit 10, an intermediate transfer belt 11, and the like.
The image forming unit 3Y includes a photosensitive drum 31Y, a charger 32Y, a developing unit 33Y, a primary transfer roller 34Y, a cleaner 35Y for cleaning the photosensitive drum 31Y, and the like disposed around the photosensitive drum 31Y. A Y-color toner image is formed on the drum 31Y.

The other image forming units 3M to 3K have the same configuration as the image forming unit 3Y, and the reference numerals are omitted in FIG.
The intermediate transfer belt 11 is an endless belt, is stretched around a driving roller 12 and a driven roller 13, and is rotationally driven in the direction of arrow A.
The optical unit 10 includes a light emitting element such as a laser diode, emits a laser beam L for forming an image of Y to K colors by a drive signal from the control unit 60, and exposes and scans the photosensitive drums 31Y to 31K.

By this exposure scanning, electrostatic latent images are formed on the photosensitive drums 31Y to 31K charged by the chargers 32Y to 32K.
The electrostatic latent images are developed by developing units 33Y to 33K, and Y to K color toner images are superimposed on the same positions on the intermediate transfer belt 11 and primarily transferred onto the photosensitive drums 31Y to 31K. It is executed at different timings.

The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 11 by the electrostatic force acting on the primary transfer rollers 34Y to 34K to form a full-color toner image, and further move toward the secondary transfer position 46.
On the other hand, the paper feed unit 4 includes a paper feed cassette 41 that stores the recording sheets S, a feed roller 42 that feeds the recording sheets S in the paper feed cassette 41 one by one onto the transport path 43, and a fed recording sheet S. Are provided with a timing roller pair 44 for taking the timing of feeding the toner to the secondary transfer position 46, and the recording sheet S is transferred from the paper feeding unit 4 to the secondary transfer position in accordance with the movement timing of the toner image on the intermediate transfer belt 11. The toner images on the intermediate transfer belt 11 are collectively transferred onto the recording sheet S by the action of the secondary transfer roller 45.

The recording sheet S that has passed the secondary transfer position 46 is conveyed to the fixing unit 5, and the toner image (unfixed image) on the recording sheet S is fixed to the recording sheet S by heating and pressurization in the fixing unit 5. Thereafter, the sheet is discharged onto the discharge tray 72 via the discharge roller pair 71.
<Fixing part>
FIG. 2 is a partial cross-sectional perspective view of the fixing unit 5.

As shown in the figure, the fixing unit 5 includes a fixing roller 150, a fixing belt 154, a belt regulating member 157, a pressure roller 160, a magnetic flux generation unit 170, and the like.
In the figure, the fixing unit 5 is drawn so that the right side of the drawing is the upward direction in FIG.
The fixing roller 150 and the pressure roller 160 are arranged in parallel. By urging the pressure roller 160 to the fixing roller 150 side by an urging mechanism (not shown), a fixing nip N is formed between the two rollers. As the recording sheet S passes through the nip N, the toner image T formed on the recording sheet S is melted and pressed to be fixed.

Details of each part will be described below.
<Magnetic flux generator>
FIG. 3A is a cross-sectional view (a cross section orthogonal to the axial direction of the fixing roller 150 (hereinafter simply referred to as “roller axial direction”)) of the main part of the fixing unit 5 in the present embodiment.
In the drawing, only one end portion of the fixing portion 5 in the roller axis direction is illustrated, but the other end portion has the same configuration.

Further, FIG. 3B shows that the urging by the pressure roller 160 of the fixing unit 5 in the present embodiment is not performed, and the temperature rise and thermal expansion caused by induction heating of the fixing belt 154 are shown. FIG. 3C is a diagram illustrating a state of the fixing roller 150 generated, and FIG. 3C is a cross-sectional view taken along a section QQ ′ in a driving state of the fixing unit 5 in the present embodiment.
As shown in FIG. 3C, the magnetic flux generator 170 has an induction coil 171, is outside the circulation path of the fixing belt 154, and is positioned at a position facing the pressure roller 160 across the fixing belt 154. Arranged along the width direction.

The induction coil 171 is connected to a drive circuit (not shown) including a high-frequency inverter, and generates a magnetic flux for heating the heat generating layer of the fixing belt 154 by supplying high-frequency power from the drive circuit.
This magnetic flux passes through a portion of the heat generating layer of the fixing belt 154 that mainly faces the induction coil 171 and generates eddy current in this portion to generate heat.

The heat of the heat generating layer is transmitted to the fixing nip N by the rotation of the fixing belt 154, so that the area of the fixing nip N (nip area) is heated.
Although not shown, a sensor for detecting the temperature of the fixing belt 154 is separately provided, and the current temperature of the fixing belt 154 is detected by a detection signal of the sensor, and the nip region is detected based on the detected temperature. The power supply to the induction coil 171 is controlled so that the temperature is maintained at a target temperature, for example, 180 [° C.].

When the sheet S passes through the fixing nip N while the temperature of the fixing nip N is maintained at the target temperature, an unfixed toner image on the sheet S is heated and pressed to be thermally fixed on the sheet S. The
<Pressure roller>
As shown in FIG. 3C, the pressure roller 160 includes a roller shaft 161 and an elastic layer 162, and is rotationally driven by a drive mechanism (not shown).

The roller shaft 161 is, for example, a cylindrical shaft having an outer diameter of 20 mm made of aluminum or the like.
The elastic layer 162 is made of, for example, silicone rubber, and is a cylindrical body having an outer diameter that is the same as the outer diameter of the fixing roller 150 and an inner diameter of 20 mm.
The hardness of the elastic layer 162 is preferably about 55 ° to 62 ° Asker hardness.

<Fixing belt>
In the fixing belt 154, a heat generating layer (not shown), a belt elastic layer (not shown), and a release layer (not shown) are laminated in order from the inside, and the entire thickness t is 0.3 mm, and the inner diameter is fixed. The endless belt is larger than the outer diameter of the roller 150.
The outer diameter of the fixing belt 154 is determined in relation to the inner diameter of a ring portion 157a (described later) of the belt regulating member 157. Details will be described later.

The heat generating layer is a metal layer that is induction-heated by the magnetic flux generated from the magnetic flux generator 170, and is made of, for example, nickel.
As the fixing belt 154 goes around, the induction-heated portion of the heat generating layer reaches the fixing nip N, where heat is conducted to the recording sheet S on which the pressing force is applied, whereby the toner on the recording sheet S is heated. It is fixed.

The belt elastic layer is, for example, an elastic layer and is made of, for example, silicone rubber.
The release layer is made of, for example, PFA and enhances the release property on the surface of the fixing belt 154.
<Fixing roller>
In the fixing roller 150, an elastic layer 152 is formed on the peripheral surface excluding both ends of the roller shaft 151.

The elastic layer 152 is a cylindrical body having an outer diameter of D _R1 mm and an inner diameter of 20 mm. The elastic layer 152 has a lower hardness than the elastic layer 162 of the pressure roller 160 and has high elasticity and high heat insulation properties, for example, silicone rubber. The sponge body.
The hardness of the elastic layer 152 is preferably about 18 ° to 24 ° Asker hardness.
Here, the diameter of the end portion in the axial direction of the elastic layer 152 is smaller than the central portion, and a predetermined space is formed between the elastic layer 152 and the fixing belt 154 at the end portion.

This is because in the region where the fixing nip N of the elastic layer 152 is formed, deformation occurs due to the pressing of the pressure roller 160, and a refuge is ensured in a portion that is pushed toward both ends in the axial direction of the roller shaft 151. .
The roller shaft 151 is, for example, a cylindrical shaft having an outer diameter of 20 mm made of aluminum or the like.

More specifically, as shown in FIG. 3A, the roller shaft 151 has a reduced diameter portion 151a having an outer diameter smaller than that of the central portion 151e at both ends.
The reduced diameter portion 151a is provided with a groove 151d extending in the circumferential direction.
A belt restricting member 157 having a hole in the center is extrapolated to the reduced diameter portion 151a, and the movement of the belt restricting member 157 in the roller axial direction is restricted by mounting the C ring 159 in the groove 151d.

The roller shaft 151 of the fixing roller 150 is pivotally supported at both ends by a frame (not shown) of the fixing device body.
In the present embodiment, the belt regulating member 157 is configured to rotate together with the roller shaft 151, but the belt regulating member 157 may be rotatably held on the roller shaft 151. In this case, the belt regulating member 157 may be supported on the roller shaft 151 via a ball bearing or the like.

<Belt regulating member>
Next, the belt regulating member 157 will be described.
As shown in FIGS. 3A, 3B, and 3C, the belt regulating member 157 is a flange-like metallic member, and is made of, for example, SUS304.
Here, the said flange shape means the shape which has a ring-shaped edge part on the outer periphery of the disk-shaped member which has a hole in the center, and says what is called a cap shape.

  An edge portion of the fixing belt 154 is brought into contact with a portion (hereinafter referred to as “disk portion”) 157b of the belt regulating member 157 corresponding to the disk-shaped member to suppress meandering of the fixing belt 154 and the ring-shaped member. The outer peripheral surface of the end portion of the fixing belt 154 is brought into contact with the inner peripheral surface of the portion (hereinafter referred to as “ring portion”) 157a so as to stabilize the circulation path of the fixing belt 154 during the belt rotation. It has become.

The belt regulating member 157 is attached to the roller shaft 151 so that the ring portion 157a is coaxial with the roller shaft 151.
<Dimensions of each part>
Hereinafter, the dimensions of each part in the fixing device will be described.
(1) The outer diameter of the fixing belt 154 and the inner diameter of the ring portion 157a First, there is no pressure on the fixing roller 150 by the pressure roller 160, and the fixing belt 154 is inductively heated to a predetermined fixing temperature (hereinafter, “ A heating non-pressurized state)), in which not only the fixing belt 154 but also the belt regulating member 157 is heated to the same extent by heat transmitted from the fixing belt 154, and thermal expansion occurs in both. That is, attention is paid to the dimensional relationship when the temperature is almost the same as the condition under which the actual fixing operation is performed.

Ideally, at this time, it is desirable that the outer peripheral surface of the end portion of the fixing belt 154 is in contact with the inner periphery of the ring portion 157a of the belt regulating member 157 over the entire circumference.
As a result, when the pressure roller 160 is actually brought into pressure contact with the fixing belt 154 to form the fixing nip portion N, the end portion of the fixing belt 154 is originally in contact with the inner periphery of the ring portion 157a. Therefore, even if a force is generated to widen the fixing nip portion N in the circumferential end portion, there is no room for deformation into an elliptical shape as shown in FIG. Most of the portion except the portion corresponding to the fixing nip portion N is guided in contact with the inner periphery of the ring portion 157a, so that the circulation path of the fixing belt 154 is stabilized and the distance from the magnetic flux generating portion 170 is increased. Heat fluctuation that does not easily fluctuate and greatly affects the fixing quality does not occur.

However, in actual dimensional design, it is necessary to consider tolerances in the manufacturing stage.
As shown in FIG. 3 (b), the inner diameter value of the ring portion 157a of the heat non-pressurized state and _{D H4,} the outer diameter value of the heat-fixing belt 154 in a non-pressurized state when the _{D H3, D H4} And _DH3 are set so as to satisfy the following relationship.
Here, the manufacturing, the inside diameter value D _R4 of the ring portion 157a has a dimensional tolerance of ± beta, The outer diameter D _H3 of the fixing belt 154 is assumed to have a dimensional tolerance of ± gamma.

If the values of this tolerance in the heating non-pressurized state are ± β ′ and ± γ ′, the maximum difference between _DH4 and _DH3 is β ′ + γ ′ which is the maximum value of the sum of the tolerances.
_Therefore, the gap between the outer periphery of the _{D H4 -D H3 = β '+} γ' by setting the design dimension _{D H3} and _{D H4} so that (Equation 1), fixing the inner circumference of the ring portion 157a belt 154 When the distance is d ₁ , it can be in the range of 0 ≦ d ₁ ≦ (β ′ + γ ′) / 2 over the entire circumference in the heating non-pressurized state.

Even in mass production, according to the current production technology, the numerical values of β and γ can be suppressed to very small values of 0.2 mm and 0.1 mm, respectively. Even so, it can be considered that β ′ and γ ′ are approximately equal to β and γ, respectively.
Then, the maximum value of the gap _{d 1} can be suppressed to (0.1 + 0.2) /2=0.15mm.

In other words, taking into consideration of the cost assumed mass production, the realistic value of the gap d _1, 0 mm or more, and the range of 0.15 mm, if such a small gap, fixing quality Can hardly be affected.
In addition, since the outer circumference of the fixing belt 154 is not larger than the inner circumference of the ring portion 157a by setting the design dimensions as described above, both ends of the fixing belt 154 are connected to the belt regulating member 157 when assembling the parts. It can be inserted into the ring portion 157a.

The value of D _H4, D _H3 in the heated non-pressurized, than the thermal expansion coefficient of each material of the fixing belt 154, a belt regulation member 157, for example, by using Equation 2 below, their production and processing The dimensions (design dimensions) D _R3 and D _R4 at the time temperature are easily determined.
(Formula 2) D _R = D _H / (K × (T _H −T _R ) +1)
K: coefficient of linear expansion of member T _H (° C.): Temperature D _H of the member in the heated state: diameter of the member in heated condition T _R: room temperature (23 ° C.)
D _R: diameter of member at normal temperature although the belt regulating member 157 and the thermal expansion coefficient Kg, when the Kb thermal expansion coefficient of the fixing belt 154, when Kg is greater than Kb, during assembly, fixing belt 154 may not enter the ring portion 157a of the belt regulating member 157. Therefore, even if Kg is substantially equal to Kb or there is a difference between them, a relationship of _{R R3} ≦ D _R4 (assembly) From the viewpoint of easiness, it is more preferable that D _R3 <D _R4 is satisfied) and that the relationship of D _H3 ≦ D _H4 is satisfied at the time of heating and non-pressurization. is there.

These specific values can be easily determined by those skilled in the art based on the actual size of the ring portion 157a of the belt regulating member 157, the required strength, and cost considerations.
The outer diameters of the fixing roller 150 and the pressure roller 160 are desirably substantially the same. As a result, when viewed from the axial direction, the fixing belt 154 is depressed in a shape almost the same as when the arc before deformation is reversed inward by the pressure applied by the pressure roller 160. Before and after the formation, the circumferential length of the fixing belt 154 existing in this region hardly changes, and the outer peripheral surface of the ring portion 157a and the outer peripheral surface of the fixing belt 154 in most other portions except the nip portion N. This is because the contact state can be maintained in the same manner as before the formation of the nip portion.

However, there is a slight difference in the outer diameters of the fixing roller 150 and the pressure roller 160, more specifically, a difference of ± 5 mm at the maximum, within a range in which the fluctuation amount of the distance from the exciting coil of the fixing belt does not exceed the allowable range. It doesn't matter.
With the above configuration, the fixing unit 5 in the present embodiment can stabilize the circulation path of the fixing belt 154 even if the fixing plate 5 is eliminated in the loose-fitting method. Therefore, the fixing quality can be kept good.

(2) Relationship between the outer diameter of the fixing roller and the inner diameter of the ring portion 157a As described above, the belt regulating member 157 is formed at both end portions of the fixing belt 154 as shown in FIGS. 3 (a) and 3 (c). The circuit route is regulated.
Since most of the fixing belt 154 is guided in contact with the inner periphery of the ring portion 157a except for the portion corresponding to the fixing nip portion N, the circulation path of the fixing belt 154 is thereby changed to that of the ring portion 157a. There is no deviation outside the inner diameter.

However, it cannot be said that there is no possibility that the circulation path of the fixing belt 154 temporarily changes toward the center due to vibration or the like.
Therefore, the inventor conducted a test and the like, and during the fixing operation, the portion of the fixing belt 154 facing the magnetic flux generator 170 is the radial direction of the fixing roller 150 (hereinafter referred to as “roller radial direction”). Even if the heating amount changes, an attempt was made to confirm the allowable range of the above-described fluctuation that does not cause large fixing unevenness that causes deterioration of fixing quality.

As a result, it was confirmed that if the fluctuation amount of the fixing belt 154 in the roller radial direction is 0.7 mm or less, the fixing unevenness does not occur and the fixing quality does not cause a problem.
Here, in a state where the temperature is the same as that during execution of the fixing operation and the influence of the pressing force from the pressure roller 160 is ignored (assumed that no pressure is applied), the ring portion of the belt regulating member 157 a value obtained by dividing the difference the _(D H4 _{-D H1)} at 2 and the outer diameter _{D H1} of the elastic layer 152 of the inner diameter _{D H4} and the fixing roller 150 157a to _{d 2,} the fixing belt 154, vibration or the like is added However, no matter how much the position changes, the fluctuation is allowed only in the range of d ₂ -t (the thickness of the fixing belt 154) in the roller radial direction.

The same can be said for the portion of the fixing belt 154 that passes through other than the nip portion N during execution of the actual fixing operation.
Therefore, the value of _{d 2 is,} to satisfy the relationship _d 2 -t ≦ 0.7 mm (Equation 3), fixing unevenness will not occur.
In this embodiment, since the thickness t of the fixing belt 154 is 0.3 mm, the value of d ₂ is 1 mm.

Furthermore, provisions inventors have, in the fixing portion 5 of the present embodiment, as described below and an outer diameter D _H1 of the elastic layer 152 of outer diameter D _H3 and the fixing roller 150 of the fixing belt 154 in the heating non-pressurized state did.
d ₃ ≦ (D _H3 −2 × t−D _H1 ) / 2 (Formula 4)
Here, “t” is the thickness of the fixing belt 154 as described above. Since the value of t is very small in this embodiment, the thermal expansion of the thickness due to heating is in a negligible range.

Also, d ₃ is to suppress thermal conduction between the outer periphery of the inner periphery and the fixing roller 150 (outer circumference of the elastic layer 152) of the fixing belt 154, required to shorten the heating time of the fixing belt 154 This is the lower limit of the gap between the two.
However, in the actual dimensional design, it is necessary to consider the tolerance in the manufacturing stage. Therefore, even if such a tolerance occurs, the value of (D _H3 −2 × t−D _H1 ) / 2 is d ₃ . A design that takes into account such dimensional tolerances, as well as the value of d ₂ , can be easily implemented by those skilled in the art.

Incidentally, the end of intensive studies of the inventors, began lead to 0.1mm as the value of _{d 3.}
Here, when _DH1 is set so that ( _DH3-2 × t- _DH1 ) = 0.1 mm, the temperature rise from the start of heating until the fixing temperature reaches 180 ° C. in the driving state of the fixing unit 5. The time was reduced to about ½ compared with the conventional fixing unit in which the fixing belt and the fixing roller are in close contact with each other.

_DH1 set as described above is the outer diameter of the elastic layer 152 of the fixing roller 150 in the heat non-pressurized state, but the dimension (design dimension) D at the temperature at the time of manufacturing and processing using Equation 2. _R1 can be determined.
<Modification>
The present invention is not limited to the above-described embodiment, and the following modifications can be implemented.

(1) In the above embodiment, the belt restricting member 157 has a flange shape. However, the belt restricting member 157 may not necessarily have a flange shape. For example, when the meandering suppression of the fixing belt 154 is realized by another mechanism, a disk is used. The part 157b is not necessary.
In that case, in order to fix the ring portion 157a to the roller shaft 151, for example, an annular member into which the roller shaft 151 can be inserted is provided, and an arm portion that connects the annular member and the ring portion 157a is provided. That's fine.

(2) In the above embodiment, the fixing belt 154 has the heat generation layer, the belt elastic layer, and the release layer laminated in this order from the inside. However, the present invention is not limited to this, and at least the heat generation layer is included. All that is required is a belt.
(3) In the above embodiment, the values of the dimensional tolerances β and γ, or δ are specifically shown. However, these values are merely examples, and are appropriately determined according to the progress of manufacturing technology.

(4) In the above embodiment, the magnetic flux generator 170 has the induction coil 171, is located outside the circulation path of the fixing belt 154, and is disposed at a position facing the pressure roller 160 across the fixing belt 154. However, the present invention is not limited to this, and it may be disposed at a location shifted from this position.
(5) In the above embodiment, the example in which the fixing device and the image forming apparatus according to the present invention are applied to a tandem color digital printer has been described. However, the present invention is not limited to this.

  Regardless of color or monochrome image formation, the fixing roller inserted loosely inside the loop path of the endless fixing belt is pressed from the outside of the loop path with the pressure roller through the fixing belt, thereby fixing the fixing nip. Any electromagnetic induction heating type fixing device configured to inductively heat the fixing belt and an image forming apparatus including the same can be applied to, for example, a copying machine, a FAX, an MFP (Multiple Function Peripheral), and the like.

  Further, the contents of the above embodiment and the above modification may be combined.

  The present invention can be widely applied to a fixing device and an image forming apparatus that heat-fix an unfixed image on a recording sheet by heating a fixing belt by induction heating.

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 3Y, 3M, 3C, 3K Image creation part 4 Paper feed part 5 Fixing part 10 Optical part 11 Intermediate transfer belt 12 Drive roller 13 Driven roller 18 Belt regulating member 31 Photosensitive drum 32 Charger 33 Developer 34 Primary transfer roller 35 Cleaner 41 Paper feed cassette 42 Feed roller 43 Conveying path 44 Timing roller pair 45 Secondary transfer roller 46 Secondary transfer position 60 Control unit 71 Discharge roller pair 72 Discharge tray 150 Fixing roller 151 Roller shaft 151a Reduced diameter portion 151d Groove 151e Central portion 152 Elastic layer 154 Fixing belt 154a Heat generation layer 154c Release layer 157 Belt regulating member 157a Ring portion 157b Disk portion 159 C ring 160 Pressure roller 161 Roller shaft 162 Elastic layer 170 Magnetic flux generation portion 171 181 ring portion

Claims (3)

The first roller loosely inserted inside the endless belt is pressed by the second roller through the belt from the outer periphery of the belt, and a fixing nip is formed between the belt surface and the second roller. And fixing the unfixed image by fixing the unfixed image by passing the sheet on which the unfixed image is formed through the fixing nip by induction heating with a high frequency magnetic field generated by an induction coil while circling the belt. A device,
The both ends of the first roller in the axial direction have flange shapes each having a ring-shaped edge, and the outer periphery of both ends of the belt is in contact with the inner surface of the ring-shaped portion, so that the outside of the belt A pair of belt regulating members that regulate the diameter are arranged,
In a state where the belt is heated to a predetermined temperature and is not pressed by the second roller, the difference between the inner diameter of the inner surface and the outer diameters of both end portions of the belt is the tolerance of the radial dimensions of both. A fixing device having a value equal to or less than a maximum value of the sum of the two.   During execution of the fixing operation, the distance between the outer peripheral surface of the belt located outside the fixing nip formation range and the inner surface in the radial direction is within a range of 0.7 mm or less. The fixing device according to claim 1, wherein an outer diameter is determined.   An image forming apparatus having the fixing device according to claim 1.

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