JP2003066745A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device and an image forming device capable of reducing the occurrence of abnormal image when a belt-fixation is performed. SOLUTION: The fixing device 1 is provided with a fixing belt 33 stretched and hung to a fixing roller 31 and a heating roller 32, and a pressurizing roller 34 provided opposing the fixing roller 31. Then the fixing device 1 heats and pressurizes an unfixed toner image (t) carried on a recording paper S by a nip N consisting of a part C wound on the pressurizing roller 34 of the fixing belt 33 and a part A where the fixing roller 31 and the pressurizing roller 32 contact with each other inserting the fixing belt 33. The fixing device has a guide member 35 arranged so as to bend the carrying path R of the fixing belt 33 and improving the tension of the fixing belt 33 at a nip entrance (g). The guide member 35 stretches and hangs the fixing belt 33 reaching between with the pressurizing roller 34 separated from the pressurizing roller 34.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus provided with a fixing device and an identification fixing device for fixing a recording material carrying a toner image, and more specifically, to an endless belt stretched between a plurality of rollers. The present invention relates to a fixing device and an image forming apparatus that fix an unfixed toner image on a recording material by a nip formed by a fixing belt and a pressure roller that contacts the fixing belt.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine, a laser beam printer, a facsimile, etc., an unfixed toner image corresponding to an original image is formed on a recording material in an image forming section, and recording is carried on the unfixed toner image. The material is heated and pressed by a fixing device to be fixed on the recording material, and a permanent image is formed on the recording material. As a fixing device used in such an image forming apparatus, there is conventionally known a fixing device which adopts a belt fixing method using a belt which rises quickly. In this fixing device, a fixing belt is stretched around at least two rollers, and a nip is formed by bringing the fixing belt and a pressure roller arranged opposite thereto into contact with each other, and a toner image is formed in this nip. A recording material such as a carried sheet is passed through, and at that time, a heating and pressing process is performed to fix the recording material.

By the way, in the fixing device disclosed in Japanese Patent Laid-Open No. 10-307496, as shown in FIG. 10, a fixing roller 100, a heating roller 110, and an endless fixing belt stretched between these rollers. A fixing roller 120 is provided to face the fixing roller 100 via the fixing belt 120. Here, the fixing belt 120 is wound around the pressure roller 130 to form a nip N between the fixing belt 120 and the pressure roller 130.
The heating roller 110 is arranged in front of the entrance g of the nip N. In this case, the fixing belt 120 having a small heat capacity
The toner is fixed on the recording material 140 that passes through the nip N after being heated in advance. The rising time is relatively short, and the wide nip width L has a characteristic that fixing at low temperature is possible. Further, the heating roller 110 of this fixing device has a halogen heater 150 therein as a heating unit for heating the fixing belt 120.
The heating roller 110 heats the fixing belt 120 by wrapping it around the fixing belt 120 at an angle. In such a fixing device, the fixing belt 120 is in contact with the fixing roller 120 while being wound around the fixing roller 120, and the fixing roller 120 and the fixing roller 120 are in contact with the fixing roller 120. By holding the nip N composed of and, stable transportability and fixing property are obtained by the nip N.

In the fixing device disclosed in Japanese Patent Laid-Open No. 9-160405, a pressing member 160 for pressing the fixing belt 120 against the pressure roller 130 at the nip entrance g is provided at the nip exit, as shown in FIG. The fixing belt 120 includes a fixing roller 100 and a pressure roller 130.
A wide nip width L is maintained by pinching with and to stabilize the image. Incidentally, JP-A-9-21860
No. 2 discloses a fixing device having the same configuration except that the conveying path of the fixing belt is bent into an acute angle by a pressing member. Further, in the fixing device disclosed in Japanese Unexamined Patent Publication No. 9-138598, at least two rollers are arranged inside the endless fixing belt, and a driving means is attached to one of these rollers and a braking means is attached to the other, and secured by both. The tension is applied to the belt by the difference in rotation so that the image quality is stabilized.

[0005]

In the fixing device of FIG. 10, the nip N formed by the fixing belt 120 and the pressure roller 130 is composed of the belt pressing portion a and the roller pressing portion b. Stable transportability and fixability can be obtained. However, the angle θ between the conveyance path R of the fixing belt 120 that extends straight from the heating roller 110 toward the nip entrance g and the conveyance path r of the recording material 140 toward the nip entrance g is extremely small, and the two paths approach each other. Is relatively large. Therefore, when the flatness of the fixing belt 120 is impaired due to waviness or slack, the unfixed toner t on the recording material 140, which approaches and faces the fixing belt 120, easily comes into contact with the fixing belt 120 before the nip N. There is a problem that the fixing belt 120 rubs the unfixed toner on the recording material 140 to cause image disturbance, and an abnormal image occurs.

In order to avoid this problem, Japanese Patent Laid-Open No. 9-160
In the case of the fixing device disclosed in Japanese Patent Application Laid-Open No. 405 or JP-A No. 9-218602, as shown in FIG. 11, the pressing member 160 folds the conveyance path R of the fixing belt 120 to convey the recording material to the vicinity of the nip entrance g. Even when r and the conveyance path R of the fixing belt are not close to each other and the fixing belt 120 is corrugated, the recording material 140 is in front of the nip N.
The contact with 20 can be reduced. However, in these cases, the pressing member 160 causes the fixing belt 120 to move to the pressure roller 1.
A pressing member pressing area A composed of a portion pressed against 30 is formed in the vicinity of the nip entrance g, and a roller pressing area C composed of a portion where the fixing roller 100 and the pressing roller 130 sandwich the fixing belt 120 is formed in the vicinity of the nip N exit. And a belt pressing area B, which is a portion where the fixing belt 120 is wound around the pressing roller 130, is formed between the pressing member pressing area A and the roller pressing area C.

In these cases, as shown in FIG. 12, the pressing member pressing area A (referred to as area A) and the roller pressing area C are shown.
In (indicated as a region C), the fixing belt 120 comes into contact with the pressure roller 130 under a relatively large pressing force (indicating a stress), but the belt pressure region B (region B) sandwiched between the two pressure regions. In addition, the fixing belt 12 is attached to the pressure roller 130.
Although 0 contacts, the pressing force is low and the tension of the fixing belt tends to be almost zero. Therefore, in the belt pressing area B, the belt and the recording material are slackened or wavy easily, the adhesion between the fixing belt and the recording material is not maintained, and the image is disturbed or wrinkled.

Further, in the case where such a structure having a long nip width L is adopted, a speed difference between the fixing belt 120 and the pressure roller 130 is apt to occur, but the fixing belt 120 and the pressure roller 13 are likely to occur.
When there is a speed difference of 0, the toner fixed halfway in the pressing member pressing area A is deviated in the belt pressing area B where the pressure is low, and is fixed again in the roller pressing area C again. Phenomenon occurs. In this case, the image is an abnormal image in which the whole or part of the image is blurred.

When a pair of rollers are pressed against a pressure roller and tension is applied to the belt between them as in the fixing device disclosed in Japanese Patent Laid-Open No. 9-138598, belt slack is suppressed and the image is stabilized. It is easy to plan. However, in this case and in the case of the fixing device disclosed in Japanese Patent Application Laid-Open No. 9-160405 or Japanese Patent Application Laid-Open No. 9-218602, the fixing roller or the pressing member is pressed against the pressure roller via the fixing belt near the nip entrance. Therefore, by suddenly pressing the unfixed toner image at this position, the contact between the belt and the recording material becomes unstable, and the image is crushed, and an abnormal image such as an image shift occurs at this point. Therefore, stable transportability and fixability cannot be obtained.

Based on the above problems, the present invention firstly reduces abnormal images such as image misalignment caused by contact between the fixing belt and the recording material due to waviness and slack of the fixing belt, and the rise time. An object of the present invention is to provide a fixing device capable of obtaining a short and stable image. Secondly, it is an object of the present invention to provide an image forming apparatus capable of preventing an abnormal image such as an image shift from occurring by performing image processing using the fixing device according to any one of claims 1 to 5. And

[0011]

In order to achieve the above-mentioned object, the invention of claim 1 provides an endless fixing belt stretched between a fixing roller and a heating roller, and the fixing belt via the fixing belt. A pressure roller is provided opposite to the fixing roller, and recording is performed by a nip including at least a portion where the fixing belt is wound around the pressure roller and a portion where the fixing roller and the pressure roller are in contact with each other across the fixing belt. In a fixing device that heats and presses an unfixed toner image carried on a material, it is arranged inside the conveyance path of the fixing belt so as to bend the conveyance path, and is a guide for increasing the tension of the fixing belt at the nip entrance. The fixing belt is provided with a member, and the fixing belt extending between the guide member and the pressure roller is stretched apart from the pressure roller. As described above, the guide member is not brought into contact with the pressure roller, but is installed at a position close to the pressure roller, and the conveyance path of the fixing belt is bent at the nip entrance, and at the same time, the belt tension is increased to fix the fixing belt. By stabilizing the belt behavior during conveyance of the paper, it suppresses the waving and slack of the belt, suppresses the interference between the fixing belt and the recording material toward the nip, reduces the image crushing, and fixes the unfixed toner image on the fixing belt. Can be prevented and the occurrence of abnormal images can be reduced,
Particularly, it can be effectively used as a fixing device for color. Preferably, the guide member may be arranged so that the conveyance path is bent at an acute angle. In this case, it is possible to more reliably suppress the interference between the fixing belt before reaching the nip and the recording material facing the nip.

According to a second aspect of the present invention, in the fixing device according to the first aspect, the guide member is a rotating body that receives a rotational load. Since the guide member is the rotating body as described above, it is easy to keep the tension of the fixing belt constant, and it is possible to reduce the occurrence of abnormal images.

According to a third aspect of the invention, in the fixing device according to the first aspect, the guide member is a fixed member, and the tension is kept constant by frictional sliding with the inner surface of the fixing belt. To do. Thus, since the guide member is the fixed member, it is possible to reduce the cost and reduce the occurrence of abnormal images. Further, the contact area with the fixing belt can be reduced, and the rising time can be shortened.

According to a fourth aspect of the invention, in the fixing device according to the third aspect, the guide member is composed of a guide member made of a heat insulating material and a reinforcing member for reinforcing the guide member. . In this way, since the guide member is heat-insulating, it is difficult to remove heat from the fixing belt, and the rising time of the fixing device can be shortened. Further, since the bending of the guide member is reduced by the reinforcing member, it is possible to stabilize the conveyance of the fixing belt and reduce the occurrence of abnormal images.

The invention of claim 5 relates to claims 1 to 4.
In the fixing device described in any one of the above, the guide member has a shape such that the center in the longitudinal direction is projected more than both ends in the longitudinal direction. In this way, by increasing the tension at the center of the belt as compared with that at both ends, it is possible to reliably reduce the slack of the belt, which tends to occur at the center of the belt, and stabilize the image. Occurrence can be reduced.

The invention of claim 6 is a fixing device for heating and pressing an unfixed toner image carried on a recording material in an image forming section in an electrophotographic system, according to any one of claims 1 to 6. A fixing device is provided. As described above, the image forming apparatus selectively adopts the fixing device according to any one of claims 1 to 5, and thereby the same effect as the adopted fixing device can be obtained also in the image forming apparatus. Therefore, it is possible to improve the commercialability of the image forming apparatus that does not cause an abnormal image such as an image shift.

[0017]

DETAILED DESCRIPTION OF THE INVENTION An image forming apparatus equipped with a fixing device and an identification fixing device according to an embodiment of the present invention will be described below. The fixing device of the present invention is a conventional electrophotographic image forming apparatus, that is, electrostatic latent image forming means for forming an electrostatic latent image on an electrostatic latent image carrier, and developing the electrostatic latent image with toner. A fixing device in an image forming apparatus including an image forming unit including a developing device for performing a toner image transfer, a transfer device for transferring the obtained toner image onto a recording material, and a fixing device for fixing an unfixed toner image on the recording material. Is adopted as. Here, other than the fixing device, as long as it does not violate the object of the present invention, a conventionally known image forming device can be adopted. The commerciality of the image forming apparatus that does not occur can be improved.

FIG. 1 shows a color copying machine 1 as an image forming apparatus. The color copying machine 1 includes a scanner section 2 for reading an original, an image processing section 3 for electrically processing an image signal output as a digital signal from the scanner section 2, and each color processed by the image processing section 3. The printer unit 5 is provided with a fixing device 4 that transfers an image onto a recording sheet S as a recording material based on the image recording information for each and fixes the unfixed toner image on the recording sheet. The scanner unit 2 has a lamp, for example, a fluorescent lamp 7, which exposes and scans a document on the document table 6. The reflected light from the document exposed and illuminated by the fluorescent lamp 7 is reflected by the mirrors 8, 9 and 10 and enters the imaging lens 11. Next, the reflected light is imaged on the dichroic prism 12 by the imaging lens 11, and is split into, for example, three types of wavelength light of red R, green G, and blue B. The separated light of each wavelength is incident on an individual light receiver, for example, CCD 13 _R, 13 _G, 13 _B. These CCDs 13 _R, 13 _{G, and} 13 _B convert incident light into digital signals and output the digital signals. The outputs are subjected to necessary processing in the image processing unit 3, and recording color information of each color, for example, black BK and yellow. Y, magenta M,
It is converted into a color information signal for cyan C recording formation.

In this embodiment, each color BK, Y, M, C
Although an example of forming four colors is shown, a color image can be created with only three colors.
Images can also be formed. In this case, the record in the figure
You can reduce the number of devices by one. The signal from the image processing unit 3 is
Laser light emitting device of each color input to the printer unit 5
14_BK, 14_C,14_M,14_YSent to. Pudding
In the example shown in the drawing, the recording unit 5 has four sets of recording devices 15_BK, 15
_C,15_M,15 _YIs attached. Each recording device 15
Are made up of the same components, simplifying the explanation.
Therefore, here, for example, the recording device 15 for cyan C is used._CTo
The other colors will be omitted. In addition, each color
For use, the same parts are designated by the same reference numerals and the subscript B
Each color is distinguished by K, M, and Y.

Recording device 15_CEmits laser light for writing
Device 14_CBesides, for example, a drum-shaped photoconductor 16_CHave
It Photoconductor 16_CAs is well known,
Charger 19_C, Laser light emitting device 14_CExposure position by
Storage and development device 17_C, Transfer charger 18_CEtc. are set in order
It has been burned. Charger charger 19_CUniformly charged by
Photoconductor 16_CAbove the laser beam emitting device 14_CTo
The latent image of the cyan light image is formed by the exposure by
Storage 17_CA visible image is formed by development with. Paper feed roller 22
The paper feed unit 20, for example, one of two paper feed cassettes
The recording paper S fed from the
Transfer belt 2
Sent to 4. Recording paper conveyed by transfer belt 24
S is a photoconductor 16 on which a visible image is formed._BK, 16_C,
16_M,16_YTo the transfer charger 1
8_BK, 18 _C,18_M,18_YThe effect of
To be copied.

The recording paper S on which the visible image is transferred is sent to a fixing device 4 described later, and the unfixed toner image t is heated and pressed by the device to be fixed, and then the paper is ejected by a paper ejection roller 23 to a paper ejection tray 27. Is ejected. In such an operation, the recording paper S is electrostatically adsorbed by the transfer belt 24 and is accurately conveyed along the belt. In addition, each of the photoconductors 16 _BK , 16 _C, 1
For 6 _{M and} 16 _Y , a reflective photosensor 2 that optically detects the amount of toner adhered to the toner image pattern
5 _BK , 25 _{C ,} 25 _M, 25 _Y are provided. The image processing unit 3 controls the operation of each unit of the printer unit 5 according to a predetermined program stored in the internal memory to write laser light emitting devices 14 _BK , 14 _C, 14.
The writing light amount (laser power) of _{M and} 14 _{Y is} , for example,
The gradation is changed from 1 to 7 values.

In the developing sleeve (for example, the developing sleeve 26 _C of the developing device 17 _C for cyan as a representative), the developing bias VB is variably controlled by the image processing section 3. In such a configuration, an image signal is output as a digital signal from the scanner unit 2, and when this signal is electrically processed by the image processing unit 3, based on the image recording information of each color from the image processing unit 3, The printer unit 5 forms an image on the recording sheet S. In addition, as in the case of such normal image formation, in the case of cyan, for example, in the case of cyan, the writing laser emitting device 14 _C , the charging charger 18 _C, and the developing device 17 _C.
Visible image pattern is formed by the sensor pattern forming means comprising a, the pattern is read to the photosensor 25 _C. Then, based on the concentration information of the visible pattern, the developing bias of the developing device 17 _C, at least one of the charging potential or the writing light quantity for writing laser beam emitter 14 _C of the photosensitive member 16 _C is controlled appropriately .

One end of the transfer belt 24 in the stretching direction,
In FIG. 1, the fixing device 4 is provided at the end opposite to the paper feeding unit 20, and the conveyance of the recording paper S to the fixing device 4 ends at the other end, that is, near the paper feeding unit 20 side. A cleaning device 28 for cleaning the paper dust or the developer attached to the surface of the transfer belt 24 is provided. The recording paper S separated from the transfer belt 22 is guided by the conveyance guide member 29 and fixes the unfixed toner image t carried on the recording paper S. Then, the recording sheet S, which has been fixed, is discharged toward the discharge tray 27 by the discharge roller 23.

Here, the transfer unit including the transfer belt 24 and the transfer charger 18 and the mechanical portion including the transfer belt cleaning device 28 and the fixing device 4 constitute a transport unit U, which is a color copying machine. 1 to the base frame by a sliding mechanism (not shown).
Is provided on the front side of the drawing so that it can be inserted into and removed from an opening (not shown) of the apparatus body. Note that the transport unit U is provided with a not-shown handle, which is stored in the apparatus main body in a locked state when the operating handle is switched to the locking position and locked when switched to the releasing position. The state is released and the device is pulled out of the main body. Next, a first embodiment of the fixing device 4 used in such a color copying machine 1 will be described.

As shown in FIGS. 1 and 2, the fixing device 4 includes a fixing roller 31 and a heating roller 32 which are arranged to face each other.
And an endless fixing belt 33 stretched around both rollers,
A pressure roller 34 that forms a nip N by being pressed against the fixing belt 33, and a roller-shaped guide member that is disposed inside the annular conveyance path R of the fixing belt 33 and at a position displaced to the transfer belt 24 side. And 35. The fixing device 4 heats the fixing belt 33 by the heating roller 32,
The fixing belt 33 is rotated in the direction of the arrow D to move the fixing belt 3
In the nip N formed by 3 and the pressure roller 34, the unfixed toner image t carried on the recording material S is heated and melted and fixed on the recording material S. Here, the fixing roller 31, the heating roller 32, the pressure roller 34, and the roller-shaped guide member 35 are pivotally attached to the fixing device base frame 36 fixed to the transport unit U side, and their respective rotation axes are arranged in parallel with each other. To be done. The transport guide member 29 is also supported by the fixing device base frame 36.

The base material of the fixing belt 33 is formed of a heat resistant resin. Materials for the heat resistant resin include polyimide, polyamide imide, polyether ketone (PEE)
K) etc. are used. The thickness of the base material is preferably 30 to 100 μm from the viewpoint of balance between heat conduction and strength. Since the surface of the fixing belt 33 comes into pressure contact with the recording material S and the unfixed toner image t, a surface layer excellent in releasing property and heat resistance is required, and a surface releasing layer such as a fluorine resin is coated. It has been configured. An elastic layer made of heat-resistant rubber such as silicone rubber or fluororubber having a thickness of 100 to 300 μm is provided under the surface release layer in order to obtain image uniformity. The heating roller 32 has a diameter of φ20 to φ30 and is made of Al.
Alternatively, a thin metal roller made of Fe and having a thickness ta of ta = 0.3 to 1.0 mm is formed, and a halogen heater 37 is provided as a heat source inside. The temperature of the heating roller 32 is detected by the temperature control element 38, and the detected temperature information is output to the image processing unit 3 so that the heating roller is controlled to have a preset constant temperature, which requires the fixing belt 33. It plays the role of heating to various temperatures.

The heating roller 32 also functions as a tension roller, and is stretched in the direction of the broken line arrow P1 in the drawing by a tension spring or the like (not shown). The fixing roller 31 is formed to have a diameter of φ20 to φ30, and is provided with an elastic layer 312 formed of a heat resistant elastic body such as foamed silicone rubber or liquid silicone rubber on the outer periphery of the Fe core metal 311 in order to obtain a nip width L. . The elastic layer 312 has a thickness of 3 to
It is about 6 mm. The surface hardness of the fixing roller 31 is Ask.
erC is about 30 to 50 Hs.

The pressure roller 34 comprises a heat-resistant elastic layer 342 made of fluorine-based rubber, silicone rubber or the like on the outer periphery of a core bar 341 made of Fe or Al, and a surface release layer 34 made of fluorine-based resin.
3 is formed. In this embodiment, the recording material S
In order to improve the toner releasability, the surface hardness of the pressure roller 34 is made harder than that of the fixing roller 31, and the fixing belt 33
The pressure roller 34 and the pressure roller 34 contact each other to form a fixing nip N having a nip width L in which both ends are curved downward. In this embodiment, the elastic layer 342 of the pressure roller 34 has a thickness of about 0.5 to 2 mm and a surface hardness of A.
It is skerC70-90Hs. It is desirable to provide a halogen heater 344 in the pressure roller 34 to accelerate the temperature rise of the pressure roller.

The fixing device 4 has a rotary drive system (not shown),
The rotary drive system transmits a rotary drive force to the pressure roller 34 by a transmission means (not shown). In addition to this, the rotational driving force may be transmitted to the fixing roller 31 in some cases. Inside the conveyance path R of the fixing belt 33, a roller-shaped guide member 35 that is biased from the nip entrance g to the transfer belt 24 side is installed.

The guide member 35 is arranged in the vicinity of the nip entrance g so as to bend the conveying path R of the fixing belt 33 at an acute angle α and at the same time increase the belt tension.
Both ends of the are supported on the fixing device base frame 36 side.

As shown in FIG. 3, the guide member 35 includes a metallic rotating shaft 351 and a roller layer 3 of a heat insulating resin around the rotating shaft 351.
However, other resin rollers or metal rollers can be used as long as the bending rigidity and the heat insulating property can be secured. 2 and 3, the guide member 35 is a resin roller layer 35.
Since 2 has a heat insulating property, the heat of the fixing belt 33 is hard to be taken, and the rising time of the fixing device can be shortened. The guide member 35 is not to be brought into contact with the pressure roller 34, but is installed separately at a position close to the pressure roller 34 and reaches between the pressure roller 34 and the fixing belt 33.
Is separated from the pressure roller 34 and stretched.

As described above, since the guide member 35 is arranged so that the conveying path is bent at the acute angle α, the fixing belt 33 is provided.
It is possible to reliably suppress the waviness of the fixing belt 33 in the vicinity of the nip entrance g where it is highly necessary to suppress the waviness, and it is possible to reliably suppress the interference between this and the recording paper S toward the nip entrance g. In the fixing device 1 as described above, the fixing roller 33 and the pressure roller 3 are sandwiched between the fixing belt 33 and the belt pressure portion a which the fixing belt 33 is in contact with while being wound around the pressure roller 34.
4 holds the nip N having a relatively large nip width L composed of the roller pressing portion b with which the roller 4 abuts. Therefore, the nip N
As a result, image crushing is reduced, deviation of the unfixed toner image t on the fixing belt 33 is prevented, and occurrence of an abnormal image is reduced to obtain stable transportability and fixability, especially for color fixing. It is effective as a device.

The roller-shaped guide member 35 here is used.
The rotation shaft 351 is rotationally loaded by a torque limiter 361 and the like, and is pivotally supported by the fixing device base frame 36. Thereby, the tension of the fixing belt 33 between the guide member 35 and the nip N formed by the fixing roller 31 and the pressure roller 34 via the fixing belt 33 can be set to be large. In this case, originally, when the tension of the belt is small in the section from the guide member 35 to the nip N, the corrugation or slack of the belt is likely to occur, and the surface of the fixing belt and the unfixed toner image t on the recording paper S rub against each other. Although an abnormal image such as an image shift may occur, here, by adopting a configuration in which a rotational load is applied by the torque limiter 361, the belt tension is maintained high at the nip entrance g, and it is stable even though the rising time is short. Image quality can be obtained. FIG. 4 shows a fixing device according to a second embodiment of the present invention. The fixing device 4a has the same configuration as that of the fixing device 4 of FIG. 2 except that the position of the heating roller 32a with respect to the guide member 35a and the fixing belt 33 is different. Are denoted by the same reference numerals and are distinguished by the subscript a.

Here, the heating roller 32a is arranged more eccentrically to the transfer belt 24 side than the heating roller 32 of FIG. 2, so that the conveyance path R of the fixing belt 33a wound around the guide member 35a has an obtuse angle β. It is arranged to increase the belt tension at the same time as it is bent. Similar to the fixing device 1, the fixing device 1a includes a fixing belt 33a that reaches between the pressure roller 34a and the tension roller 34a. Hold the nip N of the nip width L. As a result, the same effect as that of the fixing device 1, that is, the nip N having the nip width L is obtained.
Thus, the image is prevented from being crushed, the unfixed toner image t on the fixing belt 33 is prevented from being displaced, and the occurrence of an abnormal image is reduced, so that stable carrying property and fixing property are obtained. Particularly, since the guide member 35a is arranged so as to bend the conveyance path R of the fixing belt 33a at an obtuse angle β, the fixing belt 33a
Since it is stretched by bending it relatively gently,
The durability of the fixing belt 33a is improved. FIG. 5 shows a fixing device according to a third embodiment of the present invention. The fixing device 4b can be installed in the color copying machine 1 of FIG. 1 in place of the fixing device 4 of FIG. To do.

The fixing device 4b shown in FIG. 5 is similar to the fixing device 1 shown in FIG. 2, and includes a fixing roller 31b, a heating roller 32b, a fixing belt 33b, and a pressure roller 3 which are arranged to face each other.
4b and a guide member 35b disposed inside the annular conveyance path R of the fixing belt 33b and displaced to the transfer belt 24 side (right side in FIG. 5).
In the nip N formed by b and the pressure roller 34b,
The unfixed toner image t carried on the recording paper S is heated and melted,
It functions so as to be fixed on the recording paper S. Here, as shown in FIGS. 5 and 6, the guide member 35b is formed as a bar-shaped member having a substantially semicircular cross section having an arcuate projecting surface f1 continuous in the longitudinal direction, and both ends thereof are fixed. It is fixed to the device base frame 36. Projecting surface f of the guide member 35b
1 is in sliding contact with the inner surface of the fixing belt 33b, and the conveying path R of the fixing belt 33b is bent at an acute angle α by the guide member 35b.

Here again, the guide member 35b is the pressure roller 3
The fixing belt 33b is installed at a position close to the pressure roller 34b instead of abutting against the pressure roller 34b, and is stretched around the pressure roller 34b apart from the pressure roller 34b. In this way, the guide member 35b is moved to the transport route R
Is arranged so as to be bent at an acute angle α, and the guide member 35b
And the inner surface of the belt are slidably contacted with each other with an appropriate coefficient of friction, so that the fixing belt 33 is squeezed so as to be taut. This suppresses waviness of the fixing belt 33b,
The interference with the recording material S toward the nip entrance g can be surely suppressed. Here, the base material of the guide member 35b is the fixing belt 33b.
The protruding surface f1 that is in sliding contact with is formed of a material having heat resistance, friction resistance, and an appropriate friction coefficient, such as a heat resistant resin or a metal covered with glass fiber. As a result, durability can be ensured and the guide member 35b exhibits heat insulation, so that heat of the fixing belt 33b is less likely to be taken and the rise time of the fixing device can be shortened.

In the case of the fixing device 4b of FIG. 5, the guide member 3
Since 5b is fixed, there is no need for rotating parts such as bearings, and the cost can be reduced. Also, the fixing belt 3
The area in contact with 3b can be made smaller than that of the rotating body of FIG. 2, and the substantial heat capacity is reduced, which makes it easy to shorten the rise time. FIG. 7 shows a guide member 35c that can be used instead of the bar-shaped guide member 35b in the fixing device 4b of FIG. The guide member 35c is replaced with the guide member 35b, and similarly the fixing device 4 is used.
It can be applied to b, and the duplicate description is omitted here, the same parts are denoted by the same reference numerals, and they are distinguished by the subscript c. Similar to the guide member 35b of FIGS. 5 and 6, the guide member 35c is formed as a bar-shaped member having an arcuate protruding surface f1 but a substantially semicircular cross section changed, and both ends are fixed to the fixing device base frame 36. Has been done.

As shown in FIG. 7, in the substantially semicircular cross section of the guide member 35c, the protruding amount e, which is the distance between the back surface f2 and the protruding surface f1, continuously changes in the longitudinal direction of the guide member. The central portion in the longitudinal direction is projected more than both end portions. As a result, the tension of the fixing belt 33 that is in sliding contact with the central portion in the longitudinal direction becomes higher than that at both ends, and the fixing belt 33 that is particularly apt to occur.
It is possible to reduce the slack in the central portion of the belt and stabilize the belt behavior. FIG. 8 shows a fixing device according to a fifth embodiment of the present invention. This fixing device 4d can be installed in the color copying machine 1 of FIG. 1 in place of the fixing device 4b of FIG. 5. Here, duplicate description will be omitted, and the same parts will be denoted by the same reference numerals and distinguished by the subscript d. To do. The fixing device 4d in FIG. 8 is similar to the fixing device 1 in FIG. 2, and includes a fixing roller 31d, a heating roller 32d, a fixing belt 33d, a pressure roller 34d, and a fixing belt 33d which are arranged to face each other. A guide member 35d disposed inside the path R and displaced to the transfer belt 24 side (right side in FIG. 8).
In the nip N formed by the fixing belt 33d and the pressure roller 34d, the unfixed toner image t carried on the recording paper S is heated and melted and fixed on the recording paper S.

As shown in FIGS. 8 and 9, the guide member 35d is formed of a main body 351d and a reinforcing member 352d made of metal and having a rectangular cross section for supporting the main body 351d.
Both ends of are fixed to the fixing device base frame 36. The reinforcing member 352d has sufficient bending rigidity and suppresses the bending of the main body 351d due to the belt tension. The main body 351d of the guide member is formed as a bar-shaped member having a substantially semicircular cross section having an arcuate projecting surface f1 continuous in the longitudinal direction, and the surface opposite to the projecting surface f1 is a reinforcing member 352.
It is integrally joined to d. Here again, the protruding surface f1 of the guide member 35d is in sliding contact with the inner surface of the fixing belt 33d,
The conveyance path R of the fixing belt 33d by the guide member 35d
Is bent at an acute angle α. Further, the guide member 35
d is not placed in contact with the pressure roller 34d, but is installed at a position close to the pressure roller 34d, and the fixing belt 33d reaching between the pressure roller 34d and the pressure roller 34d is stretched apart from the pressure roller 34d. To do.

Since the guide member 35d has rigidity by the reinforcing member 352d, the main body 351d can be formed small, heat is not taken from the fixing belt so much, and in this respect, the rising time can be shortened. It will be easy. It should be noted that the main body 351d is formed in a shape in which the protrusion amount e is protruded in the central portion in the longitudinal direction of the guide member as compared with the both end portions similarly to the guide member 35c in FIG. 7, and the slack in the central portion of the fixing belt 33d is reduced. However, the belt behavior may be made more stable. As described above, in the color copying machine 1 as the image forming apparatus, the transfer belt 24
The recording medium S conveyed by the photoconductor 1 on which a visible image is formed.
6 _BK , 16 _C, 16 _{M , and} 16 _Y are sequentially sent, and a visible image is transferred by the action of each transfer charger 18 and then transferred to the fixing device 4 and fixed. However, instead of this, Toner images formed on each photoconductor are superposed and transferred onto an intermediate transfer belt having a horizontally extending surface, and the superposed and transferred images are collectively transferred to a recording paper as a recording material, and a visible image is transferred. The fixing device 4 of the present invention may be adopted in a color copying machine (not shown) which conveys the formed recording paper to the fixing device, and in this case, the same effect can be obtained.

Although the color copying machine 1 has been described above as an image forming apparatus, the present invention is not limited to this, and the present invention is applied to a monochromatic copying machine, a color printer, a facsimile machine, a printing machine and the like. The same effect can be obtained in these cases as well.

[0042]

As described above, according to the first aspect of the present invention, the guide member is not brought into contact with the pressure roller but is installed at a position close to the pressure roller and the fixing belt of the fixing belt is installed at the nip entrance. By bending the conveyance path and increasing the belt tension at the same time to stabilize the belt behavior during the conveyance of the fixing belt, it is possible to suppress the waviness and slack of the belt and to suppress the interference between the fixing belt and the recording paper S toward the nip. Can be reduced, deviation of the unfixed toner image t on the fixing belt can be prevented, and occurrence of an abnormal image can be reduced, and it can be effectively used particularly as a fixing device for color.

According to the second aspect of the invention, since the guide member is a rotating body, it is easy to keep the tension of the fixing belt constant, and it is possible to reduce the occurrence of abnormal images.

According to the third aspect of the invention, since the guide member is the fixed member, the cost can be reduced, and the occurrence of abnormal images can be reduced. Further, the contact area with the fixing belt can be reduced, and the rising time can be shortened.

According to the fourth aspect of the invention, since the guide member is heat-insulating, the heat of the fixing belt is hardly taken away, and the rising time of the fixing device can be shortened. Further, since the bending of the guide member is reduced by the reinforcing member, it is possible to stabilize the conveyance of the fixing belt and reduce the occurrence of abnormal images.

According to the fifth aspect of the present invention, the tension at the center of the belt is set to be larger than that at both ends, so that the slack of the belt, which is apt to occur at the center of the belt, is surely reduced to stabilize the image. Therefore, it is possible to reduce the occurrence of abnormal images.

According to a sixth aspect of the invention, by selectively adopting the fixing device according to any one of the first to fifth aspects,
The effect equivalent to that of the adopted fixing device can be similarly obtained in the image forming apparatus, and the commerciality can be improved as the image forming apparatus in which an abnormal image such as an image shift does not occur.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a color copying machine including a fixing device as an embodiment of the present invention.

FIG. 2 is an enlarged schematic configuration diagram of the fixing device in FIG.

3 is a cross-sectional view of a guide member used in the fixing device of FIG.

4 is an enlarged schematic configuration diagram of a fixing device that can be used in the color copying machine of FIG. 1 instead of the fixing device of FIG.

5 is an enlarged schematic configuration diagram of a fixing device that can be used in the color copying machine of FIG. 1 instead of the fixing device of FIG.

6 is a sectional view of a guide member used in the fixing device of FIG.

7 is a cross-sectional view of another guide member that can be used instead of the guide member used in the fixing device of FIG.

8 is an enlarged schematic configuration diagram of a fixing device that can be used in the color copying machine of FIG. 1 instead of the fixing device of FIG.

9 is a cross-sectional view of a guide member used in the fixing device of FIG.

FIG. 10 is a schematic configuration diagram of a conventional fixing device.

FIG. 11 is a schematic configuration diagram of another conventional fixing device.

12 is a characteristic diagram of a pressing force distribution at the nip position of the fixing device of FIG.

[Explanation of symbols]

1 Color Copier 4 Fixing Device 31 Fixing Roller 32 Heating Roller 33 Fixing Belt 34 Pressing Rollers 35 to 35c Guide Member g Nip Entrance t Unfixed Toner Image N Nip A Part C where Fixing Roller and Pressing Roller Abut C Pressing Part wound around roller R Conveying path of fixing belt S Recording paper

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shigeo Kurotaka             1-3-3 Nakamagome, Ota-ku, Tokyo, stock             Company Ricoh (72) Inventor Kiyoshi Oshima             1-3-3 Nakamagome, Ota-ku, Tokyo, stock             Company Ricoh (72) Inventor Takashi Fujita             1-3-3 Nakamagome, Ota-ku, Tokyo, stock             Company Ricoh (72) Inventor Satoshi Baba             1-3-3 Nakamagome, Ota-ku, Tokyo, stock             Company Ricoh (72) Inventor Naoshi Kikuchi             1-3-3 Nakamagome, Ota-ku, Tokyo, stock             Company Ricoh (72) Inventor Jun Nakato             1-3-3 Nakamagome, Ota-ku, Tokyo, stock             Company Ricoh F-term (reference) 2H033 AA01 BA09 BA11 BA12 BA25                       BB18 BB28

Claims (6)

[Claims] 1. An endless fixing belt stretched between a fixing roller and a heating roller, and a pressure roller provided to face the fixing roller via the fixing belt. At least the fixing belt is provided. In a fixing device for heating and pressing an unfixed toner image carried on a recording material by a nip composed of a portion wound around a pressure roller and a portion where a fixing roller and a pressure roller are in contact with each other with a fixing belt interposed therebetween, The fixing belt is provided inside the conveyance path of the fixing belt and is arranged to bend the conveyance path, and has a guide member for increasing the tension of the fixing belt at the nip entrance, and the guide member reaches between the pressure roller and the fixing belt. The fixing device is characterized in that the fixing device is tensioned from the pressure roller. 2. The fixing device according to claim 1, wherein the guide member is a rotating body that receives a rotational load. 3. The fixing device according to claim 1, wherein the guide member is a fixed member, and the tension is kept constant by frictional sliding with the inner surface of the fixing belt. 4. The fixing device according to claim 3, wherein the guide member includes a guide member made of a heat insulating material and a reinforcing member that reinforces the guide member. 5. The fixing device according to any one of claims 1 to 4, wherein the guide member has a shape such that the center in the longitudinal direction projects more than both ends in the longitudinal direction. Fixing device characterized by. 6. A fixing device according to claim 1, which is a fixing device for heating and pressing an unfixed toner image carried on a recording material in an image forming section in an electrophotographic system. An image forming apparatus characterized by the above.