JP2000066542A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of image quality by preventing recording paper from slipping at a nip part between a heating roller and a pressure roller even in the case of transferring a toner image on a recording paper which is made thin and whose frictional force is low by synchronizingly driving the heating roller and the pressure roller. SOLUTION: Gears 43a and 44b are provided at the end parts of the rotary shafts of the heating roller 37 and the pressure roller 38, and the gears 43a and 44b are meshed. Also, the gear 43a is connected with a driving motor 45 through a gear group 46 consisting of plural gears, and the driving force of the driving motor 45 is transmitted to the gear 43a through the gear group 46. Thus, the driving force from the driving motor 45 is transmitted to the gear 44b through the gear 43a, and the heating roller 37 and the pressure roller 38 are synchronized and driven. Also, the driving motor 45 is connected to a photoreceptive unit such as a photoreceptive drum and a transfer roller through a specified gear group, so that the photoreceptive unit is also driven by the driving motor 45.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device,
More specifically, the present invention relates to a fixing device used in an electrophotographic facsimile device, a printer device, a copying machine, etc. More specifically, a recording paper on which a toner image is transferred by an image transfer member is nipped by a heating roller and a pressure roller. The present invention relates to a fixing device configured to fix toner on recording paper by being conveyed.

[0002]

2. Description of the Related Art Generally, when a toner image is transferred onto a recording sheet by an image transfer member such as a photosensitive drum or a transfer roller, the toner image is fixed on the recording sheet by a fixing member including a heating roller and a pressure roller. I am trying to do it. Specifically, as shown in FIG. 6, a fixing heater 2 is built in the heating roller 1, and a pressing roller 3 is slidably pressed against the heating roller 1 by a pressing spring 4 with a constant pressing force. I have. As shown in FIG. 7, the driving force from the driving motor 6 is transmitted to the heating roller 1 by a reduction mechanism 5 including a plurality of gears. It is designed to go around with you.

The drive motor 1 drives a photosensitive unit such as a photosensitive drum and a transfer roller, and is connected to the photosensitive unit by a speed reduction mechanism (not shown). In FIG. 7, P is a recording sheet sandwiched between the heating roller 1 and the pressing roller 3. In such an apparatus, before the recording paper fed from the nip between the photosensitive drum and the transfer roller is sandwiched between the nips of the heating roller 1 and the pressure roller 3, the recording paper is upstream of both rollers. After forming a loop as a certain margin, the toner image is fixed on the recording paper by being sandwiched between the nip portions of the heating roller 1 and the pressure roller 3.

In order to form such a loop, the conveying speed of the heating roller 1 is set to be lower than the conveying speed of the photosensitive drum. In this manner, the loop is formed on the recording paper. When the recording paper is pulled too much by the heating roller 1 and the pressure roller 3, the toner image cannot be normally transferred to the recording paper by the photosensitive drum, or the recording paper is pulled too much by the heating roller 1 and the pressure roller 3. The occurrence of an abnormal image due to the rubbing of the image or the like is prevented.

In other words, the transport speed of the heating roller 1 has a great effect on the image quality, and if a large deviation occurs in the transport speed between the photosensitive drum and the heating roller 1, the transport speed between the heating roller 1 and the photosensitive drum is increased. A large loop occurs on the path, and the image on the recording paper is rubbed by the guide plate constituting the conveyance path, or the recording paper is excessively pulled by the heating roller 1 and the pressure roller 3 so that the toner image is formed on the recording paper by the photosensitive drum. Is not transferred normally.

Therefore, at present, the diameter of the heating roller 1 is reduced to the working limit (± 0.03) with respect to the pressure roller 3 in order to reduce the dispersion of the conveying speed.
Is driven to minimize variations in the transport speed.

[0007]

However, in such a conventional fixing device, the heating roller 1 and the heating roller 1 are driven by the heating roller 1 even if the conveying speed of the heating roller 1 is controlled. At the nip portion between the heating roller 1 and the pressure roller 3, the heating roller 1 may slip with respect to the pressure roller 3, which may cause image deterioration.

[0008] Factors of such slip include the following points. The heating roller 1 is a roller in which an aluminum pipe is coated with Teflon, and the conveying force (frictional force) on the surface is much lower than that of a normal rubber roller. The reason for this is to prevent the toner from adhering to the heating roller 1 since the image surface faces the heating roller 1 when the toner image is fixed.
At present there is no alternative. The pressure roller 3 slidably contacting the heating roller 1 is configured to rotate together with the heating roller 1 by frictional contact,
The accompanying load becomes large due to bearing friction on the pressure roller 3 side, an increase in the nip width for securing the fixing rate, or inertia of the roller itself. Actually, even when the recording paper is not interposed, the linear velocity in the tangential direction of the pressure roller 3 may slip with respect to the heating roller 1 and may be reduced. Since the roller having a larger frictional force than the heating roller 1 has a greater conveyance frictional force for the recording paper, the recording paper is more likely to slip on the heating roller 1 than on the pressure roller 3.

As a result, if an image is to be transferred to a recording paper made of a thin paper having a low coefficient of friction, the recording paper is more likely to slip on the heating roller 1 than the pressure roller 3, Since it is difficult for the roller 3 to rotate with respect to the heating roller 1, the heating roller 1 loses the conveyance force of the recording paper, and the conveyance speed in the fixing unit varies. Therefore, the present invention can prevent the recording paper from slipping at the nip portion between the heating roller and the pressure roller even when a toner image is transferred to a recording paper that is thin and has a low frictional force. It is an object of the present invention to provide a fixing device that can prevent the fixing device from lowering.

[0010]

According to the first aspect of the present invention,
According to another aspect of the present invention, there is provided a fixing device provided in an image forming apparatus, the fixing device including a heating roller and a pressure roller that is in sliding contact with the heating roller, and a toner image is transferred by an image transfer member. In a fixing device that fixes the toner on the recording paper by nipping and transporting the recording paper between the heating roller and the pressure roller, the heating roller and the pressure roller are driven synchronously. And

In this case, since the heating roller and the pressure roller are driven in synchronization with each other, when the toner image is transferred to a recording sheet which is thin and has a low frictional force, the heating roller and the pressure roller are improved in order to improve the fixing rate and the like. Even if the contact area of the pressure roller is increased, it is possible to prevent the recording paper from slipping at the nip portion between the pressure roller and the heating roller, and the conveyance speed greatly varies between the image transfer member and the fixing device. Can be prevented.

Therefore, it is possible to prevent a large loop from being generated on the conveying path between the heating roller and the photosensitive drum, and to pull the recording paper excessively by the heating roller and the pressure roller to record by the photosensitive drum. It is possible to prevent a problem that a toner image cannot be normally transferred to paper, and to prevent image quality from deteriorating.

According to a second aspect of the present invention, in order to solve the above-mentioned problem, in the first aspect of the present invention, a driving force transmitting means for transmitting a driving force from the heating roller to the pressing roller is provided. I have. The reason for this will be described. When driving the pressure roller in synchronization with the heating roller, where to find the supply source of the driving source is a problem. In the current drive of the heating roller, a drive motor for driving the photoconductor unit is used as a common drive source as shown in FIG. 7, but a common drive source is used in order to suppress variations in linear speed with each unit. Is desirable.

According to the second aspect of the present invention, by providing a driving force transmitting means for directly transmitting a driving force from the heating roller to the pressure roller, the driving roller is connected to the heating roller by a common driving source with other units. The pressure roller is driven in synchronization with the heating roller and the pressure roller to obtain a stable transport force and a stable transport speed. According to a third aspect of the present invention, in order to solve the above-mentioned problem, in the first or second aspect of the present invention, a contact force between a contact surface of the heating roller and a contact surface of the pressure roller is increased. It is characterized in that a contact force increasing means is provided.

The reason for this will be described. The pressure roller is essentially a roller that must follow the heating roller completely synchronously with no variation in linear speed, so when driving the pressure roller, the heating roller and the linear speed are completely synchronized. I have to do it. However, since a rubber material having a low hardness is used for the pressure roller to satisfy conditions such as a fixing rate, the pressure roller usually has a nip width (contact area) of about 1 mm to 4 mm on a contact surface with the heating roller.

Since the nip width is delicately affected by the pressing force and environmental conditions, the distance between the recording paper conveying surface of the nip and the axes of the heating roller and the pressure roller fluctuates, and the accurate rotation of the pressure roller itself is achieved. Difficult to set numbers. Therefore, when the driving force is directly transmitted from the heating roller to the pressure roller, it is difficult to sufficiently synchronize the heating roller and the pressure roller.

Therefore, according to the third aspect of the present invention, the contact surface between the heating roller and the pressure roller is provided with contact force increasing means for increasing the contact force between the contact surfaces of the two rollers. By applying the driving force directly to the pressure roller, the fluctuation factors (environment, hardness variation,
The rotation of the heating roller and the pressure roller can be controlled synchronously by suppressing the fluctuation of the number of rotations caused by the pressure error and the like, so that the heating roller and the pressure roller can obtain more stable conveyance force and conveyance speed. We were able to do it.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 show a first embodiment of a fixing device according to the present invention, and show an example in which the fixing device is mounted on a copying machine. The fixing device may be mounted on an image forming apparatus such as a printer device and a facsimile device other than the copying machine.

First, the configuration will be described. In FIG. 1, 11
Denotes a copying machine, and a paper feed tray 12 is provided on an upper surface of the copying machine 11.
Is provided. The paper feed tray 12 is configured to hold a document bundle composed of a plurality of documents. After the document bundle is fed by a pickup roller 13, a separation roller 14 that rotates clockwise and a clockwise rotation After the uppermost document is separated by the rotating reverse roller 15, a CCD (Charge Cou
After the image surface is read by a reading sensor 18 such as a pled device, the sheet is discharged onto a sheet discharge tray 20 by a sheet discharge roller pair 19.

The image data read by the reading sensor 18 is photoelectrically converted and sent to the optical writing unit 21. The optical writing unit 21 irradiates an optical signal corresponding to image data onto a photosensitive drum (image transfer member) 25 via lenses 23a and 23b and mirrors 24a and 24b while being swung by a polygon mirror 22. I have.

An outer peripheral surface of the photosensitive drum 25 is uniformly charged by a charger 26, and an electrostatic latent image corresponding to an optical signal emitted from the optical writing unit 21 is formed on the photosensitive drum 25. After the formation, a toner image is attached to the electrostatic latent image from the developing device 27, so that a visible image corresponding to the image data is transferred as a toner image. The image is transferred onto the recording paper P supplied to the nip between the photosensitive drum 25 and the transfer roller 28 facing the photosensitive drum 25. Specifically, a large number of recording papers P are stored in a paper feed cut 29, and when the recording papers P stored in the paper feed cassette 29 are fed by the paper feed roller 30, After being conveyed, it is supplied to the nip between the photosensitive drum 25 and the transfer roller 28 while being timed by the pair of registration rollers 32. At this time, by applying a voltage to the transfer roller 28, a toner image is transferred from the photosensitive drum 25 to the recording paper P.

The recording paper P on which the toner image has been transferred is conveyed to a fixing device 33, where the toner image is fixed by the fixing device 33, and then discharged by a discharge roller pair 34 provided below the discharge tray 20. The paper is discharged to the paper tray 35. The toner remaining on the photosensitive drum 25 is collected by a cleaning device 36 having a collecting blade and a collecting roller (not shown).

On the other hand, the fixing device 33 has a heating roller 37 and a pressure roller 38 as shown in FIGS. The heating roller 37 is composed of a roller in which an aluminum tube is coated with Teflon, and has a fixing heater 39 built therein. The pressure roller 38 is composed of a roller in which a tube is coated on rubber, and a pressure spring
The pressure roller 40 makes pressure contact with the heating roller 37.

A thermistor 41 is in contact with the heating roller 37, the temperature is detected by the thermistor 41, and the fixing heater 39 controls the fixing temperature to be about 200 ° C. The heating roller 37
A thermostat 42 is provided on the outer periphery of the fixing roller 39. When the temperature of the heating roller 37 becomes excessively high, control is performed such that the power of the fixing heater 39 is turned off by the thermistor 37 to lower the temperature. ing.

On the other hand, gears 43a and 44b are provided at the ends of the rotating shafts 43 and 44 of the heating roller 37 and the pressure roller 38, and the gears 43a and 44b mesh with each other. Also, gear
43a is a drive motor via a gear group 46 comprising a plurality of gears.
45, and the driving force of the driving motor 45 is
Through the gear 43a. Therefore, the driving force from the driving motor 45 is transmitted to the gear 44a via the gear 43a, and the heating roller 37 and the pressure roller 38 are driven in synchronization. The gears 43a, 44
a constitutes a driving force transmitting means.

The drive motor 45 is connected to photosensitive units such as the photosensitive drum 25 and the transfer roller 28 via a gear group (not shown). The photosensitive unit is also driven by the drive motor 45. Next, the operation will be described. The recording paper P on which the image has been transferred by the photosensitive drum 25 and the transfer roller 28 is transported toward the fixing device 33. At this time, since the toner on the recording paper P is in an unstable state in which only the image is laid, the conveyance of the heating roller 37 is performed in order to prevent the deterioration of the image on the photosensitive drum 25 and the fixing device 33. The speed is set slightly lower than the transport speed of the photosensitive drum 25.
For this reason, the original conveyed to the fixing device 33 is a photosensitive drum.
A loop is formed between 25 and the fixing device 33.

In this state, the recording paper P is nipped by the nip portion between the heating roller 37 and the pressure roller 38 and conveyed, so that the toner image is fixed on the recording paper P. Further, since the pressure roller 38 is brought into pressure contact with the heating roller 37 by the pressure spring 40, the recording paper P is stably conveyed by the heating roller 37 and the pressure roller 38, and the heating roller 37 and the pressure roller 38 As a result, the toner image cannot be normally transferred to the recording paper P by the photosensitive drum 25 due to excessive pulling of the recording paper P, or the toner image is rubbed by excessively pulling the recording paper P by the heating roller 37 and the pressure roller 38. Thus, it is possible to prevent the occurrence of an abnormal image due to the above.

Here, the pressing roller 38 is
The recording paper P is stably conveyed and the toner image is fixed by bringing the recording paper P into stable contact with the heating roller 37 under pressure. However, in general, the fixing rate is determined by the pressing force of the pressing roller 38 and the rubber hardness. (Nip width) and the fixing temperature. However, conventionally, the pressing roller 38 is
When the pressing force of the pressure roller 38 and the rubber hardness (nip width) are increased in order to improve the fixing rate, the rotation load of the pressure roller 38 increases. Slip between the recording paper P and the heating roller 37 is likely to occur due to the difference in contact force between the two rollers 37 and 38. In addition, if the fixing temperature is increased, safety and transportability of the recording paper P (curl and There is a limit from the viewpoint of wrinkles).

In this embodiment, the heating roller 37 and the rotating shafts 43 and 44 of the pressure roller 38 are connected by gears 43a and 44a, and the driving force of the drive motor 45 is applied to the heating roller 37 and the pressure roller.
38, the rollers 37 and 38 are synchronized, so that even when a toner image is transferred to a recording sheet P that is thin and has low frictional force, the heating roller 37 and the heating roller 37 are added to increase the fixing rate. Even if the contact area of the pressure roller 38 is increased, the recording paper P can be prevented from slipping at the nip portion between the pressure roller 38 and the heating roller 37, and the conveyance speed between the photosensitive drum 25 and the fixing device 33 can be reduced. It is possible to prevent large variations.

Therefore, the heating roller 37 and the photosensitive drum 25
A large loop can be prevented from occurring on the transport path between the heating roller 37 and the pressure roller.
38 prevents the occurrence of a problem that the toner image cannot be normally transferred to the recording paper P by the photosensitive drum 25 due to excessive pulling of the recording paper P, thereby preventing the image quality from deteriorating. Can be.

On the other hand, when the pressure roller 38 is driven in synchronization with the heating roller 37, the drive source thereof is constituted by the drive motor 45 for driving the photoconductor unit. And the heating roller 37 and the pressing roller 38 can provide a stable conveyance force and a stable conveyance speed. In this embodiment, the gears 43a, 44a
By connecting the rotating shafts 43 and 44 with both rollers
Although 37 and 38 are synchronized, a drive belt may be used instead as shown in FIG.

In FIG. 4, reference numeral 51 denotes a belt as driving force driving means.
Is wound around a pulley 52 provided at an end of the heating roller 37 and is wound around an end of the heating roller 37. The driving force of the heating roller 37 is transmitted to the pressure roller 38 via the belt 51. The pressure roller 38 is driven in synchronization with the heating roller 37. Also,
The belt 51 is wound around an idler pulley 53 for tension adjustment as driving force transmission means.
A constant tension is applied by a spring (not shown) provided at 53. For this reason, a stable driving force is always applied to the pressure roller 38 even when the distance between the axes of the heating roller 37 and the pressure roller 38 fluctuates.

The reason why the distance between the axes fluctuates is that, in order to secure the nip width from conditions such as the fixing rate, the pressure roller
Since the pressure roller 38 is made of a soft rubber material and the pressure roller 38 is brought into pressure contact with the heating roller 37 by the pressure spring 40, the distance between the axes of the rollers 37 and 38 is the spring pressure tolerance,
The reason for this is that the distance slightly varies due to the environment, machine-to-machine variation, and the like. In the present embodiment, the idler pulley 53 takes into account the variation in the center distance.

In addition, instead of the belt 51 being wound around the heating roller 37, a pulley is provided on the rotating shaft 43 of the heating roller 37,
It may be wound around this pulley. In any case, since the heating roller 37 has a high temperature of about 200 ° C., the belt 51 needs to be a heat-resistant belt. FIG. 5 is a diagram showing a second embodiment of a fixing device according to the present invention. The same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

Since the pressure roller 38 is originally a roller that must follow the heating roller 37 completely and synchronously with no variation in linear speed, the driving of the heating roller 37 And the linear velocity must be completely synchronized. However, since the pressure roller 38 is made of a rubber material having a low hardness in order to satisfy conditions such as a fixing rate, the pressure roller 38 usually has a nip width (contact area) of about 1 mm to 4 mm on a contact surface with the heating roller. .

The nip width is delicately influenced by the pressing force and environmental conditions.
And the distance between the axes of the pressure roller 38 fluctuates,
38 It is difficult to set the exact speed of itself. For this reason, the rotating shaft 43 of the heating roller 37 and the rotating shaft of the pressing roller 38
When transmitting the driving force directly to 44, the heating roller 37
It is difficult to sufficiently synchronize the pressure roller 38 with the pressure roller 38.

For this reason, in this embodiment, the heating roller 37
Thus, a contact force increasing means for increasing the contact force between the contact surfaces of the rollers 37 and 38 is provided to the contact surface of the pressure roller 38 and the pressure roller 38. That is, as shown in FIG. 5, the Teflon at the end of the heating roller 37 is peeled to expose the aluminum surface (black portion) 60, and the tube at the end of the pressure roller 38 is peeled to remove the rubber surface (black portion). By applying the driving force directly to the pressure roller 38 from the contact surface of the heating roller 37 by directly contacting the aluminum surface 60 and the rubber surface 61 with the exposed portion 61 exposed, the fluctuation factors ( Environment, hardness variation, pressure error, etc.) to suppress fluctuations in the number of rotations, thereby enabling the heating roller 37 and the pressure roller 38 to be driven synchronously.
With the heating roller 37 and the pressure roller 38, a more stable transport force and transport speed can be obtained.

In this embodiment, the aluminum surface 60, which is the exposed contact surface between the heating roller 37 and the pressure roller 38, and the rubber surface
61 constitutes a contact force increasing means for increasing the contact force of the contact surface of the heating roller 37 and the pressure roller 38. The contact force increasing means is not limited to this, but a knurl is formed on the aluminum surface of the heating roller 37, and the knurl is brought into contact with the pressure roller 38, or the friction coefficient between the heating roller 37 and the pressure roller 38 is increased. May be attached.

[0039]

According to the first aspect of the present invention, since the heating roller and the pressure roller are driven synchronously, when a toner image is transferred to a thin recording paper having low frictional force,
Even if the contact area between the heating roller and the pressure roller is increased in order to improve the fixing rate and the like, the recording paper can be prevented from slipping at the nip portion between the pressure roller and the heating roller. It is possible to prevent a large variation in the transport speed between the two.

Therefore, it is possible to prevent a large loop from being generated on the conveyance path between the heating roller and the photosensitive drum, and to pull the recording paper excessively by the heating roller and the pressure roller, thereby performing recording by the photosensitive drum. It is possible to prevent a problem that a toner image cannot be normally transferred to paper, and to prevent image quality from deteriorating.

According to the second aspect of the present invention, by providing the driving force transmitting means for directly transmitting the driving force from the heating roller to the pressure roller, the driving roller is connected to the heating roller by a common driving source with other units. The pressure roller can be driven synchronously, and a stable conveyance force and a stable conveyance speed can be obtained by the heating roller and the pressure roller. According to the third aspect of the present invention, the contact surface between the heating roller and the pressure roller is provided with a contact force increasing means for increasing the contact force between the contact surfaces of the two rollers, and the pressure roller is moved from the contact surface of the heating roller to the pressure roller. Since the driving force is applied directly to the heating roller, the fluctuation of the rotation speed caused by the fluctuation factors (environment, hardness variation, pressure error, etc.) on the pressure roller side is suppressed, and the heating roller and the pressure roller are synchronized. It can be driven, and a more stable transport force and transport speed can be obtained by the heating roller and the pressure roller.

[Brief description of the drawings]

FIG. 1 is a view showing a first embodiment of a fixing device according to the present invention, and is a schematic view of a copying machine equipped with the fixing device.

FIG. 2 is a configuration diagram of a fixing device according to the first embodiment.

FIG. 3 is a perspective view of a heating roller, a pressure roller, and a mechanism for transmitting a driving force to both rollers according to the first embodiment.

FIG. 4 is a diagram showing another mode of the driving force transmission mechanism of the first embodiment.

FIG. 5 is a diagram showing a second embodiment of the fixing device according to the present invention, and is a perspective view of a heating roller and a pressure roller having a contact force increasing unit.

FIG. 6 is a perspective view of a conventional heating roller and pressure roller.

FIG. 7 is a diagram illustrating a mechanism for transmitting a driving force to a heating roller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Copier (image forming apparatus) 25 Photoreceptor drum (image transfer member) 33 Fixing device 37 Heating roller 38 Pressure roller 43a, 44a Pulley (driving force transmitting means) 51 Belt (driving force transmitting means) 53 Idler pulley (driving) Force transmission means) 60 Aluminum surface (contact force increasing means) 61 Rubber surface (contact force increasing means) P Recording paper

Claims (3)

[Claims] 1. A fixing device provided in an image forming apparatus, comprising: a heating roller; and a pressure roller which is slidably contacted with the heating roller, and a recording sheet on which a toner image is transferred by an image transfer member. Fixing the toner on the recording paper by nipping and transporting the toner between the heating roller and the pressure roller, wherein the heating roller and the pressure roller are driven synchronously. apparatus. 2. The fixing device according to claim 1, further comprising a driving force transmitting unit that transmits driving force from the heating roller to the pressing roller. 3. A contact surface between the heating roller and the pressure roller,
The fixing device according to claim 1, further comprising a contact force increasing unit configured to increase a contact force between contact surfaces of the two rollers.