JP2003091184A - Fixing device and image forming apparatus having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent, at a low cost, engagement frequency transfer displacement due to paper vibration at the engagement frequency of the gear of the fixing device which results from the situation in which paper is pulled by a fixing device and tension is applied to the paper between a transfer section and a fixing section, and to prevent a fixing film and paper from being wrinkled. SOLUTION: A double-helical gear or the like is used as the drive input part (pressure roller gear) of the fixing device, thereby preventing thrust force and setting an engagement ratio to 2 or greater.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for fixing a toner image transferred onto a sheet material such as paper or a resin sheet to the sheet material, and a copying machine including the fixing device.
The present invention relates to an image forming apparatus such as a P and a facsimile.

[0002]

2. Description of the Related Art In a fixing device, a heat roller having a rod-shaped heater inserted therein and a pressure roller having an elastic body such as silicone rubber formed around a cored bar are arranged in parallel and press-contacted to each other. The nip portion is formed by elastically deforming, and the recording medium on which the toner image is transferred is passed through the nip portion of the roller pair to fix the toner image on the recording medium by heat and pressure.

Gears are attached to the heat roller,
Rotational force is received from a drive source via a gear train or the like. The meshing ratio between the gear mounted on the heat roller and the gear meshing with it is usually about 1.5 to 1.7 when the spur gear is used, and is usually 2 or more when the helical gear is used.

In order for the fixing device to be ready for use at the request of the user, it is necessary to keep the heat roller at a constant temperature.

However, in this fixing device, since the heat capacity of the heat roller is large, in order to always keep the temperature constant, it is necessary to keep the heater energized even when the device is in the standby state, and the energy efficiency is poor.

Therefore, instead of the heat roller, a long and narrow sheet heater is arranged inside a thin resin film formed in a tubular shape, and the sheet heater is opposed to and pressed against the pressure roller, so-called on-demand. There is a mold fixing device.

Since the on-demand type fixing device uses a thin film, its heat capacity is smaller than that of the heat roller type fixing device. Therefore, when the fixing device is used, current can be immediately applied to the planar heater to reach a desired temperature. It is possible to heat.

Therefore, it is not necessary to energize the heater in the standby state, and the energy efficiency is remarkably better than that of the heat roller type fixing device.

On-demand type fixing devices are roughly classified into
There are a method of giving rotational drive to the film and a method of giving rotational drive to the pressure roller.

In the system in which the film is rotationally driven, the speed of the film, which should move at the same speed as the recording medium, can be kept constant, but when the film is rotated, the film shifts in the longitudinal direction. A mechanism for returning the lean is required, and the cost of the device is relatively high.

In the system in which the pressure roller is rotationally driven,
By using a slightly thick film, the edge of the film can be received by the frame of the fixing device to prevent the film from slipping, while the pressure roller is an elastic body, so if it is used continuously, the heat from the heater Accordingly, there is a problem that the outer diameter gradually increases with temperature, and the conveyance speed of the recording medium in the fixing device also gradually increases with temperature.

If the conveying speed of the recording medium in the fixing device becomes high, the recording medium is pulled by the fixing device, and therefore the trailing edge of the recording medium may cause a toner image formed on the electrophotographic photosensitive drum to be removed. If the recording medium is transferred to the recording medium, the recording medium will be tense between the transferring unit and the fixing unit, and when the recording medium is vibrated by the fixing device, the vibration is transferred to the transferring unit. Then, an image defect such as a transfer deviation occurs in which the position where the toner image is transferred on the recording medium is displaced from the position where the toner image should be transferred.

In order to solve this problem, the distance between the transfer section and the nip section of the fixing device is conventionally increased to about 200 mm,
In some cases, the conveyance speed of the fixing device is set to be several percent slower than the process speed with respect to the conveyance speed of the recording medium (so-called process speed) at the transfer portion.

The speed difference between the two is eliminated by forming a loop in the recording medium between the transfer portion and the nip portion of the fixing device, and the fixing device does not pull the recording medium in the transfer portion, so that the transfer deviation occurs. It is preventing.

However, in recent years, recording is performed in order to shorten the so-called first copy time from when the image formation start command is issued to when the first image-formed medium is obtained, the jam of the recording medium, and the downsizing of the apparatus. The number of image forming apparatuses in which the paper passing path from the medium storage section to the discharge port is shortened is increasing.

In these devices, the latent image is written on the electrophotographic photosensitive drum based on the data of the original read by the image reading unit or the image data sent from the computer, and the latent image is developed by the toner. The distance between the transfer portion for transferring the toner image formed on the recording medium to the recording medium and the nip portion for the fixing device for fixing the toner image transferred on the recording medium to the recording medium by heat and pressure is about 200 mm in the conventional device. There was around, but about 100 ~
The length is shortened to about 120 mm, and a sufficient space for forming a loop of the recording medium cannot be provided between the transfer unit and the fixing device.

According to an experiment conducted by the present inventor, when the distance between the transfer portion and the nip portion of the fixing device is about 120 mm or less and the meshing ratio of the gears of the driving portion of the pressure roller is low, the phenomenon of transfer deviation is remarkable. Will appear.

Therefore, the speed of the fixing film is detected, and the rotation speed of the pressure roller is controlled so that the speed of the fixing film (that is, the speed of the recording medium) becomes constant, and the recording medium is provided between the image forming section and the fixing device. There are things that prevent you from being overwhelmed.

[0019]

However, the image forming apparatus having the above configuration has the following problems.

At the meshing frequency of the gears of the drive section of the fixing device, the speed of the roller on the side where the drive is input fluctuates slightly, and as a result, the recording medium vibrates minutely. This phenomenon is remarkable when a spur gear is used.

In the conventional image forming apparatus in which the distance between the transfer portion and the nip portion (fixing portion) of the fixing device is relatively long, a loop is formed in the recording medium between the transfer portion and the fixing portion as described above. Even if the recording medium vibrates minutely in the fixing unit by the driving unit of the fixing device, the vibration is not transmitted to the transfer unit.

However, in the image forming apparatus in which the distance between the transfer portion and the fixing portion is short, a sufficient loop cannot be formed in the recording medium, so that the vibration of the meshing frequency of the gears of the driving portion of the fixing device propagates to the transfer portion. It is easy and causes the transfer deviation.

Particularly in the case of an on-demand type fixing device of the pressure roller drive type, the conveying speed of the recording medium in the fixing portion is likely to fluctuate, so that the fixing device is driven when the recording medium tends to be pulled by the fixing device. The transfer deviation of the meshing frequency of the gears of the part is a problem.

Even when the speed of the pressure roller is controlled as described above, there is always an error with respect to the process speed due to the number of speed control steps, the control response, the accuracy of the transport speed detection mechanism, etc. In some cases, the recording medium may momentarily be pulled, and the recording medium is likely to vibrate at the meshing frequency of the gear that drives the pressure roller, and therefore the meshing frequency transfer deviation easily occurs.

Further, when a helical gear is used as the drive unit of the fixing device, the vibration of the gear meshing frequency in the drive unit is suppressed to a small level, so that the problem of transfer deviation is unlikely to occur.

However, when the helical gear is used, a thrust force corresponding to the load torque and the twist angle of the gear is generated.

Since the fixing device presses the roller pair or the planar heater and the pressure roller with the spring, the load torque is generally large, and hence the thrust force generated on the roller to which the helical gear is attached is also large.

When a large thrust force acts on the roller, it is necessary to reinforce the fluid of the fixing device in order to receive it and to select an expensive material for the bearing of the roller, which is not easily scraped, which causes a cost increase. Was there.

Further, if a helical gear is used for the drive unit of the on-demand type fixing device, thrust force is always generated in the roller, and there is a problem that the probability of wrinkling occurring in the recording medium or the thin film increases.

Therefore, the present invention has been made to solve the above problems, and an object thereof is to prevent image defects at the meshing frequency of the gears of the drive section of the fixing device.

It is another object of the present invention to reduce the cost required for generating the thrust force by not generating the thrust force in the drive unit.

Another object of the present invention is to significantly reduce the probability that wrinkles will occur in the recording medium or the thin film in the on-demand type fixing device by not generating thrust force in the drive section.

[0033]

According to another aspect of the present invention, there is provided a fixing device having a heating element and at least one roller for fixing a toner image transferred onto a recording medium using heat and pressure. In, the input of rotational drive to the roller is performed by a gear, and the driven gear attached to the roller and the drive gear meshing with the driven gear are not gears that generate thrust force by drive transmission, but the driven gear and the drive The gear meshing ratio is characterized by being 2 or more.

The invention of claim 2 is characterized in that, in the invention of claim 1, both the driven gear and the drive gear are helical gears.

The invention of claim 3 is characterized in that, in the invention of claim 1, both the driven gear and the drive gear are composed of two gears which are coaxially arranged with their teeth being out of phase. .

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, the fixing device includes one pressure roller and a cylindrical thin film having a sheet heating element disposed therein.
6. The invention according to claim 5, wherein the pressure roller and the thin film are arranged in parallel and a fixing operation is performed by passing a recording medium having a toner image transferred through a nip portion formed by applying pressure. 5. The electrophotographic image forming apparatus according to claim 1, wherein the electrophotographic photosensitive drum, a transfer unit that transfers the toner image formed on the electrophotographic photosensitive drum onto a recording medium, and the electrophotographic photosensitive drum according to claim 1. It is characterized by having a fixing device.

According to a sixth aspect of the invention, in the fifth aspect, the distance between the transfer portion and the nip portion of the fixing device is 12
It is characterized by being 0 mm or less.

According to a seventh aspect of the invention, in the fifth or sixth aspect of the invention, the drive source for driving the electrophotographic photosensitive drum and the drive source for driving the fixing device are different.

In the image forming apparatus according to the invention of claim 8, the fixing device comprises one pressure roller and a cylindrical thin film having a sheet heating element inside, which are arranged in parallel and face each other. The pressure roller has a speed detection means for detecting the speed of the thin film, and the pressure roller receives a drive from a drive source by a gear train, and the speed of the drive source is a signal from the speed detection means. It is characterized by being controlled based on the above.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) First, the overall structure of the image forming apparatus main body will be described with reference to FIG.

A book manuscript such as a book, cardboard, curl paper or a sheet manuscript is placed on the platen glass 202 with the manuscript surface facing downward, and the manuscript pressure plate 203 presses the back surface to set the manuscript in a stationary state and read it. When a start key (not shown) is pressed, the scanning system light source 201 scans the lower part of the platen glass 202 in the direction of arrow a in FIG. 7 while irradiating the original surface with light.

The light applied to the original is reflected in accordance with the image information of the original and is imaged on the CCD 206 via a plurality of reflecting mirrors and lenses 205 as shown by the optical path 204, and the image information is converted into an electric signal. To be converted.

An automatic document feeder is attached instead of the document pressing plate 203, and when documents are set on the automatic document feeder, the set documents are separated one by one and placed on the platen glass 202. The document is conveyed with the side facing down.

The document conveyed by the automatic document feeder is read out from the platen glass after the image information is read in the same manner as the document manually set on the platen glass. The image information converted into an electric signal by the CCD 206 is subjected to signal processing as necessary, and then transmitted to the laser scanner 111.

Here, the main body of the image forming apparatus functions as a copying machine when a processing signal of the image processing section is input to the laser scanner 111, and functions as a printer when an output signal of a personal computer or the like is input.

If a transmission signal from another facsimile device is input to the laser scanner 111 or a processing signal of the image processing section is transmitted to another facsimile device, it functions as a facsimile device.

On the other hand, a sheet cassette 101 is attached to the lower part of the main body of the image forming apparatus.

The sheets housed in the cassette 101 are semi-circular pickup rollers 10 which serve as a feeding rotary member.
When 2 rotates once, it is paid out one by one from the separation claw 103. Even when two or more sheets are fed from the separation claw 103 at one time, that is, when so-called double feeding occurs, the feed roller 104 rotates in the sheet conveying direction.
And the retard roller 105 that rotates in the reverse direction with respect to the feed roller 104 cooperate to separate the sheets one by one.

The sheet separated as described above is conveyed by the conveying roller pair 106 and guided to the registration roller 107 which is stopped.

The sheet is stopped at the registration roller 10
7, the skew is corrected by forming a loop, and then the registration roller 107 starts to rotate at a predetermined timing to be fed to the image forming unit in synchronization with the image forming operation. .

The image forming unit is the electrophotographic photosensitive drum 11
2. An image writing optical system 113, a developing device 114, a primary charging device 115, a transfer charging device 116 and the like. Then, the laser scanner 111 is formed on the surface of the photosensitive drum 112 uniformly charged by the primary charger 115.
A laser beam corresponding to the image information emitted from the image scanning optical system 113 is scanned by the image writing optical system 113 to form a latent image, and a toner image is formed on the latent image by the developing device 114.
A transfer charger 116 transfers a toner image onto the sheet conveyed by the registration rollers 107 in synchronization with the rotation of the photosensitive drum 112.

The sheet on which the toner image has been transferred is conveyed to the fixing device 118 along the guide plate 117, heated and pressed to fix the toner image on the sheet surface, and then the discharge roller 119 discharges the sheet to the discharge tray 120. It is discharged and loaded.

In this image forming apparatus, the motor for driving the image forming portion such as the electrophotographic photosensitive drum 112 and the developing device 114 is different from the motor for driving the fixing device 118.

Next, the fixing device will be described with reference to FIG.

FIG. 1 is a sectional view of a fixing device to which the first embodiment of the present invention is applied.

In FIG. 1, 11 is a pressure roller, 12 is a planar heater, 13 is a cylindrical thin film made of resin, and a fluorine coating layer is formed on the surface.
The pressure roller 11 is formed by molding a silicone sponge 11b around an aluminum cored bar 11a into a roller shape, and covering the outer peripheral surface with a modified PFA tube 11c. The surface has excellent elasticity.

The planar heater 12 is adhered to the heater holder 14, and the heater holder 14 is arranged in parallel with the pressure roller 11 with the thin film 13 sandwiched by the spring 15 and pressed against the pressure roller 11. When the heater holder 14 including the planar heater 12 is pressed against the pressure roller 11, the silicone rubber layer 11b of the pressure roller 11 is elastically deformed,
A nip 16 having a certain width is formed between the pressure roller 11 and the thin film 13.

FIG. 2 is a side view of the drive portion of the fixing device shown in FIG. 1, and is a view of FIG. 1 seen from the right side (upstream side in the sheet conveying direction). In FIG. 2, some parts such as the heater holder 14 and the spring 15 are omitted.

A driven gear 17 is attached near the end of the core metal of the pressure roller 11 and meshes with the drive gear 18. The pressure roller 11 is rotated counterclockwise in FIG.

Here, both the driven gear 17 and the drive gear 18 are helical gears, and the meshing ratio is 2 or more.

In the case of this embodiment, the driven gear 17 has a module 1, the number of teeth is 27, the pressure angle is 20 °, and the twist angle is 20 °, and the drive gear 18 is the module 1, the number of teeth 21 and the pressure angle is 2.
Since the angle is 0 °, the twist angle is 20 °, and the meshing tooth width is 8, the meshing ratio is 2.35.

FIG. 3 is a side view showing the driven gear 17 and the drive gear 18 used in this embodiment.

A cylindrical portion 17c having the same pitch circle diameter as that of the gear is provided between the right portion 17a of the tooth trace of the driven gear 17 and the left portion 17b of the helical direction. Similarly, a cylindrical portion 18c having a diameter equal to the pitch circle of the gear is provided between the portion 18a on the left side of the tooth trace of the drive gear 18 and the portion 18b on the right side of the twist direction.

When the driven gear 17 and the drive gear 18 are meshed with each other, the cylindrical portions 17c and 18c of the respective gears come into contact with each other, and the backlash between the driven gear 17 and the drive gear 18 is guaranteed. The portion 17a in which the driven gear 17 has a rightward twist direction
The drive gear 18 meshes with the left portion 18a of the drive gear 18, and the driven gear 17 meshes with the left portion 17b of the drive gear 18, and the drive gear 18 twists with the right portion 18b.

Since the core of the pressure roller 11 receives the heat of the sheet heater 12 and becomes high in temperature, the driven gear 17 is made of a resin having a high heat resistant temperature such as PPS. The drive gear 18 meshes with the fixing drive motor 19 via a gear train (not shown).

The sheet heater 12 is energized and heated at a required timing, and the recording medium on which the toner image has been transferred in the image forming portion is passed through the nip portion 16 in the direction of arrow b shown in FIG. Thus, the toner image on the recording medium is permanently fixed on the recording medium.

The thin film 13 is rotationally driven by frictional force via the recording medium passing through the nip, and its speed is almost the same as the speed of the recording medium when passing through the nip portion. A reflection mark 20 having a surface reflectance sufficiently different from that of the surface layer of the thin film 13 is formed in the non-sheet passing area of the thin film 13.

The silicone rubber portion of the pressure roller 11 thermally expands under the influence of the heat of the sheet heater 12, and the diameter of the pressure roller 11 increases. Therefore, if the fixing drive motor 19 is rotated at a constant speed, the conveyance speed of the recording medium will increase with time.

By projecting light onto the reflection mark 20, detecting the reflected light with a sensor (not shown), and measuring the time interval at which the reflected light is obtained, the actual recording medium when passing through the nip portion is measured. The transport speed can be detected.

By controlling the speed of the fixing drive motor 19 based on the signal thus detected, it is possible to keep the conveyance speed of the recording medium in the nip portion substantially constant.

The pressure roller 11 has a gear 17 for driving it.
The speed fluctuates slightly at the meshing frequency of one tooth of No. 18 and 18, and the vibration propagates to the recording medium.

Even if the speed of the fixing drive motor 19 is controlled, the fixing is temporarily performed with respect to the conveyance speed of the recording medium in the image forming section unless stepless control is performed or due to a problem of control responsiveness or the like. In some cases, the conveyance speed of the recording medium in the set becomes high.

In such a state, since the recording medium is stretched between the fixing portion and the transfer portion, the vibration of the recording medium easily propagates to the transfer portion, and therefore the transfer deviation of the meshing frequency of the driven gear 17 is prevented. Easy to wake up.

According to the study by the present inventor, when the spur gears are used for the driven gear 17 and the drive gear 18 as in the prior art and the meshing ratio is about 1.5 to 1.7, the conveying speed of the recording medium in the fixing portion is increased. Is about 0.5 to 1% faster than the conveyance speed of the recording medium at the transfer portion, transfer deviation of the gear meshing frequency occurs.

On the other hand, as shown in this embodiment, when the meshing ratio is set to 2 or more, the conveying speed of the recording medium in the fixing section becomes about 2% faster than the conveying speed of the recording medium in the transfer section. However, no transfer deviation occurs and a good output image can be obtained.

Further, since the use of the helical gear eliminates the thrust force generated when the helical gear is used, the casing of the fixing device is reinforced or pressed to receive the thrust force. It is no longer necessary to select an expensive material for the roller bearing that is difficult to scrape, and it is possible to reduce the cost required for these measures.

Further, since the thrust force does not act on the pressure roller, it is possible to greatly reduce the possibility that wrinkles are generated on the recording medium or the thin film 13.

In the present embodiment, an example of using a helical gear in which two helical gear parts having different twisting directions are integrally molded has been described. However, as shown in FIG. 4, two helical gears having different twisting directions are used. It is apparent that the same effect can be obtained even if the helical gear is formed by using the helical gears 17a, 17b or 18a, 18b.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG.

FIG. 5 is a side view of the drive portion of the fixing device to which the second embodiment of the present invention is applied, and is a view of the fixing device as seen from the upstream side in the sheet conveying direction. In FIG. 5, as in FIG. 2, some parts such as the heater holder 14 and the spring 15 are omitted. The description of the place having the same configuration as that of the first embodiment will be omitted.

A driven gear 17 is attached near the end of the core metal of the pressure roller 11 and meshes with the drive gear 18. The driven gear 17 and the drive gear 18 are composed of two gear portions 17a, 17b and 18a, 18b, respectively, as shown in FIG. Two gear parts 17a, 17
Reference numerals b or 18a, 18b denote two spur gears having the same number of modules and the same number of teeth, which are integrated by shifting the phase in the tooth tip direction by 1/2.

Spur gear pairs 17a, 18a and 17b, 1
Since the meshing ratio of 8b is always 1 or more, the meshing ratio of the driven gear 17 and the drive gear 18 having this shape is always 2 or more.

In the case of this embodiment, the thrust force does not act on the pressure roller 11 as in the case of the second embodiment, so it is not necessary to consider the influence of the thrust force as described above. In addition, since the twist angle direction of a helical gear is reversed near the center of the gear tooth width direction, when molding integrally, the structure of the mold for molding the gear becomes complicated, and the structure from the mold to the gear While the method of taking out the mold becomes complicated, the structure of the mold can be simplified by using the gear of the present embodiment as long as the parting line is provided between the two gear parts. Is possible.

In this embodiment, an example of using a gear in which two spur gear portions are integrally formed is described, but a driven gear,
It is clear that even if two spur gears for each of the drive gears are mounted on the shaft with their tooth tips displaced, the same effect can be obtained.

Further, the deviation amount of the two spur gear portions in the direction of the addendum is not limited to 1/2 tooth, and the deviation amounts of the driving gear side and the driven gear side are equal, and the two gear parts are simultaneously engaged. It's good to meet. In the first and second embodiments, the so-called pressure roller driving type on-demand type fixing device has been described, but it may be used for a film driving type on-demand type fixing device or a heat roller type fixing device. Is clear.

Further, the numerical values of the specifications of the gears such as the module of the gear, the number of teeth, the pressure angle, the helix angle, the tooth width, etc. shown in Examples 1 and 2 are merely examples, and the present invention is not limited to these.

[0088]

As described above with reference to the embodiments, according to the present invention, the toner image developed on the electrophotographic photosensitive drum is transferred to the recording medium, and the transfer portion is transferred to the recording medium. In an image forming apparatus with a short distance from the fixing unit that permanently fixes the toner image on the recording medium, the paper vibrates at the meshing frequency of the gears that drive the heat roller or the pressure roller, and the vibration propagates through the recording medium and the frequency It is possible to prevent the occurrence of image defects such as transfer deviation in the above.

In particular, in the case of a fixing device in which drive is input to the pressure roller, the outer diameter of the pressure roller tends to increase due to thermal expansion, and the conveyance speed of the recording medium tends to gradually increase. In such a case, it is particularly effective in preventing the occurrence of transfer deviation.

Since thrust force is not generated in the gears even if the drive force is transmitted, the casing of the fixing device is reinforced in order to receive the thrust force, and the bearing material of the pressure roller is not easily scraped and is expensive. This eliminates the need for them and makes it possible to reduce the costs that were required for these measures.

Further, in the pressure roller drive type on-demand type fixing device, since the thrust force does not act on the pressure roller, it is possible to greatly reduce the possibility that wrinkles are generated in the recording medium or the thin film 13.

[Brief description of drawings]

FIG. 1 is a sectional view of a fixing device to which a first embodiment of the present invention is applied.

FIG. 2 is a side view showing a driving unit of the fixing device to which the first embodiment of the present invention is applied.

FIG. 3 is a side view of a gear used in the first embodiment of the present invention.

FIG. 4 is a side view showing a drive unit of a fixing device to which the first embodiment of the present invention is applied, using two pairs of helical gears.

FIG. 5 is a side view showing a driving unit of a fixing device to which a second embodiment of the present invention is applied.

FIG. 6 is a perspective view of a gear used in the second embodiment of the present invention.

FIG. 7 is a sectional view of an electrophotographic copying machine.

[Explanation of symbols]

101 sheet cassette 102 pickup roller 103 Separated nail 104 Feed roller 105 retard roller

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H033 AA15 AA30 BA11 BA25 BA26                       BB29 BB37 BB38 BE03 CA13                       CA40                 2H071 CA01 CA05 DA09 DA12 DA26                       DA27 DA31 DA32 EA04                 3J103 AA02 AA74 BA03 BA43 CA01                       FA09 FA18 GA02 GA57 GA58                       GA60

Claims (8)

[Claims] 1. A fixing device having a heating element and at least one roller for fixing a toner image transferred onto a recording medium by using heat and pressure, wherein a rotational drive is input to the roller by a gear. The driven gear mounted on the roller and the drive gear that meshes with the driven gear are not gears that generate thrust force due to drive transmission, and the engagement ratio between the driven gear and the drive gear is 2 or more. Fixing device. 2. The fixing device according to claim 1, wherein the driven gear and the drive gear are both helical gears. 3. The fixing device according to claim 1, wherein both the driven gear and the drive gear are composed of two gears that are coaxially arranged with their teeth being out of phase. 4. The fixing device includes one pressure roller and a cylindrical thin film having a planar heating element inside, and the pressure roller and the thin film are arranged in parallel.
The fixing device according to claim 1, 2 or 3, wherein a fixing operation is performed by passing a recording medium having a toner image transferred through a nip portion formed by applying pressure. 5. The fixing device according to claim 1, further comprising: an electrophotographic photosensitive drum, a transfer unit that transfers a toner image formed on the electrophotographic photosensitive drum onto a recording medium. An electrophotographic image forming apparatus having: 6. The distance between the transfer portion and the nip portion of the fixing device is 120 mm or less.
The electrophotographic image forming apparatus described in 1. 7. The image forming apparatus according to claim 5, wherein a drive source for driving the electrophotographic photosensitive drum is different from a drive source for driving the fixing device. 8. The fixing device comprises one pressure roller and a cylindrical thin film having a sheet heating element disposed inside and arranged in parallel to face each other, and the pressure is applied. Drive speed is input to the pressure roller from a drive source by a gear train, and the speed of the drive source is controlled based on a signal from the speed detection means. The image forming apparatus according to claim 7,