JP2000330417A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a good image in either one of cases where recording material is normal paper that is relatively hard to slip or where the recording material is one that is relatively easy to slip. SOLUTION: In this image forming device, a fixing roll 10 and a press roll 20 that are of different hardness are brought into a pressurized contact, a fixing device passing the recording material with a toner image transferred on it through the pressure contact part N of the rolls formed in a projected shape on the relatively soft fixing roll side, when seen from an axial direction of the roll, and fixing that toner image to the recording material is provided and a driving switch over means 40 where transmission of driving force is possible to only one of the rolls 10 or 20 from a motor 30 is provided in between the rolls and the motor 30 driving them.

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 such as a printer, a facsimile, a copying machine, etc., capable of forming a toner image on a recording material such as paper by using an electrophotographic technique. In particular, the present invention relates to a technique for driving a roller in the fixing device.

[0002]

2. Description of the Related Art In general, an image forming apparatus for forming a toner image on a recording material such as paper by using an electrophotographic technique includes a photoconductor which is driven to rotate, and an electrostatic latent image formed on the surface by exposing the photoconductor. Exposure means for forming an image, developing means for developing the electrostatic latent image into a toner image, transfer means for transferring the toner image to a recording material, and a recording material on which the toner image has been transferred by the transfer means And a fixing device for fixing the toner image on the recording material by heating while passing through the recording material.

FIG. 3 is a schematic diagram showing a transfer section 1 and a fixing device 2 in a general image forming apparatus. Fixing device 2
Normally has a fixing roller 2a having a heat source and a pressing roller 2b pressed against the fixing roller 2a by an urging force of a spring or the like (not shown), and these two rollers 2a, 2b
The recording material S to which the toner image has been transferred by the transfer unit 1 is heated while being nipped and conveyed by the pressure contact portion N to fuse and fix the toner image on the recording material S onto the recording material S. . In such a fixing device, two rollers 2a,
If there is a peripheral speed difference in 2b, the toner image on the recording material S passing through the pressure contact portion N is rubbed, and the image is disturbed. Therefore, the two rollers are not driven. A configuration in which only the roller is driven and the other roller is driven by the other roller is employed. Further, if the method of heating the fixing roller 2a takes a long time for the initial heating, the fixing belt 3 wound around the roller 2a is heated. Fusing devices are known. It is also known that at least one of the two rollers 2a and 2b is a roller having an elastic layer in order to increase the width (length in the moving direction of the recording material) W of the pressing portion N. Usually, in order to prevent the recording material S from being wound around the fixing roller 2a (or the fixing belt 3), the shape of the press contact portion N is fixed as seen from the axial direction of the roller as shown in FIG. The fixing roller 2a is configured to be softer than the pressure roller 2b so as to be convex toward the roller 2a.

[0004]

In a recent image forming apparatus, as a recording material to be formed with an image, a relatively slippery recording material such as a relatively slippery recording material, for example, a synthetic resin sheet ( For example, a transparent sheet for OHP) and glossy paper have been used. In such a situation, the above-described conventional technique has the following problems.

[0005] The relatively soft fixing roller 2a has a large amount of thermal deformation, so that its radius greatly fluctuates due to a temperature difference. Therefore, when the fixing roller 2a is driven, the recording material S
The transfer speed of the transfer unit 1 also greatly changes due to a temperature change.
The difference between the conveyance speed of the recording material S and the conveyance speed of the recording material S greatly varies. Therefore, particularly when the recording material S is a relatively long sheet, the recording material S is moved between the fixing device 2 and the transfer unit 1. In some cases, the recording material S may be pulled or may sag greatly, and an image formed on the recording material S may be defective.

On the other hand, since the relatively hard pressure roller 2b has a small amount of thermal deformation, the above-described problem does not occur. However, when the pressure roller 2b is driven, the recording material S is relatively slippery, for example,
If the sheet is a synthetic resin sheet or glossy paper, there is a problem that slipping is likely to occur on the front and back of the recording material S, and slip marks are likely to remain on the image. In particular, in a belt fixing device in which a pair of rollers are pressed against each other via the fixing belt 3, the above-described slip is likely to occur.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a good recording medium in both cases where the recording material is relatively slippery and the recording material is relatively slippery. An object of the present invention is to provide an image forming apparatus capable of forming an image.

[0008]

According to a first aspect of the present invention, there is provided an image forming apparatus, comprising: a transfer portion for transferring a toner image onto a recording material; and a pair of rollers having different hardnesses are pressed against each other. When viewed from the axial direction of the roller, the pressure contact portion between the rollers formed in a convex shape on the relatively soft roller side,
An image forming apparatus comprising: a fixing device that fixes the toner image on the recording material through the recording material on which the toner image has been transferred, wherein a fixing device is provided between the pair of rollers and a driving source that drives these rollers. And a drive switching means for selectively transmitting the driving force from the driving source to only one of the rollers. According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the pair of rollers are pressed against each other via a heated fixing belt.

[0009]

According to the image forming apparatus of the first aspect, the recording material onto which the toner image has been transferred at the transfer portion passes through the pressure contact portion between the pair of rollers in the fixing device, so that the toner image is formed. Fixes on recording material. The pair of rollers have different hardnesses, and the pressure contact portion is formed in a convex shape on the relatively soft roller side when viewed from the axial direction of the roller, so that the recording material is wound around the relatively soft roller. It becomes difficult. Then, between the pair of rollers and a drive source that drives these rollers, a drive switching unit that can selectively transmit the driving force from the drive source to only one of the rollers is provided. Because of the provision, the following operation and effect can be obtained. That is, when the recording material is relatively slippery ordinary paper, the driving force from the driving source can be transmitted to only the relatively hard roller by the drive switching means, and can be driven (relatively). Soft rollers follow relatively hard rollers). Since a relatively hard roller has a small amount of thermal deformation, a change in radius due to a temperature difference is small. Therefore, when a relatively hard roller is driven, the conveyance speed of the recording material by the fixing device is also less affected by the temperature change, and the conveyance speed difference between the conveyance speed of the recording material by the transfer unit is also reduced. Therefore, even if the recording material is relatively long paper, it is difficult for the recording material to be pulled between the fixing device and the transfer unit or to be largely slackened. Defects are less likely to occur in the image formed thereon. On the other hand, when the recording material is relatively slippery, the driving force from the driving source is transmitted to only the relatively soft roller by the drive switching means, and this can be driven (the relatively hard roller). Follows a relatively soft roller). When a relatively soft roller is driven, slipping is less likely to occur between the recording material and the roller, and slip marks are less likely to occur on the image. Slip is less likely to occur because a relatively hard roller is driven and a relatively hard roller is driven through the recording material than when a relatively hard roller is driven and a relatively soft roller is driven through the recording material. This is because less frictional force is required between the roller and the recording material in the case where is driven. As described above, according to the image forming apparatus of the first aspect, by switching the drive roller according to the type of the recording material, the recording material is relatively slippery when the recording material is relatively slippery. A good image can be formed in any of the slippery cases. According to the image forming apparatus of the second aspect, in the image forming apparatus of the first aspect, the pair of rollers are pressed against each other via a heated fixing belt. The recording material thus passed passes through a pressure contact portion between a fixing belt in a fixing device and a roller pressed against the surface thereof, so that the toner image is fixed on the recording material. Since the heat capacity of the fixing belt is smaller than that of the roller, the initial heating time can be reduced. As described above, if a relatively hard roller is driven in a configuration in which a pair of rollers are pressed against each other via a fixing belt, as described above, the recording material is relatively slippery. In this case, the slip is likely to occur on the front and back of the recording material. However, according to the image forming apparatus of the second aspect, when the recording material is relatively slippery, the driving force from the driving source is driven. By transmitting only the relatively soft roller by the switching means and driving it (the fixing belt and the relatively hard roller follow the relatively soft roller), by driving the relatively soft roller, Slip between the recording material and the roller and the fixing belt is less likely to occur, and slip marks are less likely to occur on the image. That is, the configuration according to the first aspect is particularly effective when the pair of rollers are pressed against each other via the fixing belt.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIGS. 1A and 1B are views showing a fixing device in an image forming apparatus according to a first embodiment of the present invention. FIG. 1A is a schematic perspective view, and FIGS. FIG.

In FIG. 1A, 10 and 20 are a pair of rollers, 10 is a fixing roller, and 20 is a pressure roller.

The fixing roller 10 includes a core member 12 having a shaft 11 at an end and an elastic layer 1 provided around the core member 12.
3 and a surface layer 14 provided on the surface thereof and having excellent releasability from recording material and toner. Core material 1
2, a heat source (not shown) is provided.

The pressure roller 20 includes a core member 22 having a shaft 21 at an end and an elastic layer 2 provided around the core member 22.
3 and a surface layer 24 provided on the surface thereof and having excellent releasability from recording materials and toner. Core material 2
2, a heat source (not shown) is provided. The elastic layer 23 of the pressure roller 20 corresponds to the elastic layer 1 of the fixing roller 10.
The fixing roller 10 is made of an elastic material that is harder than that of the fixing roller 3, or is made thinner than the elastic layer 13 of the fixing roller 10. In this embodiment, the elastic layer 23 of the pressure roller 20 is made of an elastic material that is harder than the elastic layer 13 of the fixing roller 10 and is thinner than the elastic layer 13 of the fixing roller 10. Therefore, the pressure roller 20 is configured to be harder than the fixing roller 10.

In this embodiment, the axis between the fixing roller 10 and the pressure roller 20 is fixed by a frame (not shown). That is, the fixing roller 10 and the pressure roller 2
The shafts 11 and 21 of the fixing roller 10 are fixed so as not to be movable in the radial direction. Is pressed. The press contact portion N
Since the elastic layer 13 of the fixing roller 10 is thicker and more easily deformed than the elastic layer 23 of the pressure roller 20, the fixing roller 10
It is formed in a convex shape on the side (this point is the same as the press contact portion N in FIG. 3).

Reference numeral 30 denotes a motor as a driving source for driving the fixing roller 10 or the pressure roller 20 to rotate.
0, the driving force from the motor 30 is applied to the rollers 20,
Drive switching means 40 is provided for selectively transmitting to only one of the rollers 30. The drive switching means 40 according to this embodiment includes an electromagnetic clutch 4
1 and 42 and a control unit described later. A drive gear 32 is fixed to an output shaft 31 of the motor 30, and a transmission gear 33 meshes with the drive gear 32. The transmission gear 33 is fixed to a transmission shaft 34, and the transmission shaft 34 is connected to an input shaft 41a of one electromagnetic clutch 41.
(See FIGS. (B) and (c)). Then, the output shaft 41b of the electromagnetic clutch 41 (see FIGS. (B) and (c)).
Are connected to the shaft 11 of the fixing roller 10. The output shaft 31 of the motor 30 is connected to the other electromagnetic clutch 4.
2 is connected to an input shaft 42a (see FIGS. 2B and 2C), and an output shaft 42b of the electromagnetic clutch 42 (see FIG. 2B).
(See (c)) is connected to the shaft 21 of the pressure roller 20. The electromagnetic clutches 41 and 42 are respectively connected to an operation circuit controlled by a control unit (not shown) of the image forming apparatus in which the fixing device is incorporated, and as shown in FIG. The input shaft (41a or 42ab) and the output shaft (41b or 42b)
b) is connected (turned on), or the connection is cut off (turned off).

That is, the drive switching means 40 is as shown in FIG.
As shown in FIG. 5, when the other electromagnetic clutch 42 is in the ON state, the one electromagnetic clutch 41 is in the OFF state, and the driving force from the motor 30 is transmitted only to the pressure roller 20. 20 is driven to rotate, and when one of the electromagnetic clutches 41 is in the ON state, as shown in FIG.
In the FF state, the driving force from the motor 30 is
It is possible that the fixing roller 10 is driven to rotate by transmitting only to 0. Therefore,
As shown in FIG. 2B, when the pressure roller 20 is driven, one of the electromagnetic clutches 41 is in the OFF state, so that the fixing roller 10 rotates following the pressure roller 20 and rotates. As shown in c), when the fixing roller 10 is driven, the other electromagnetic clutch 42 is in the OFF state, so that the pressure roller 20 rotates following the fixing roller 10. The switching operation of the drive switching unit 40 as described above can be automatically performed by the above-described control unit. That is, when a paper type is selected by an operation of an operation unit (not shown) of the image forming apparatus or a host computer (for example, a personal computer) (not shown) to which the image forming apparatus is connected, the switching is performed according to the selected paper type. Actions can be taken. For example, when a relatively slippery recording material such as plain paper is selected by a user's operation, the pressure roller 20 is driven, and a relatively slippery recording material such as a synthetic resin sheet (for example, an OHP sheet) or glossy paper is used. When a material is selected, the fixing roller 10
Can be driven.

In the image forming apparatus, the above-described fixing device is disposed at a stage subsequent to a transfer section for transferring a toner image to a recording material (see FIG. 3).

According to the image forming apparatus of this embodiment,
The following operation and effect can be obtained. The recording material on which the toner image has been transferred by the transfer unit is a pair of rollers 1 in a fixing device.
The toner image is fixed on the recording material by passing through the pressure contact portion N between 0 and 20. A pair of rollers 10,
20 are different in hardness, and the pressure contact portion N is formed in a convex shape on the side of the fixing roller 10 which is relatively soft when viewed from the axial direction of the roller, so that recording on the fixing roller 10 which is a relatively soft roller is performed. Winding of the material is less likely to occur.

A motor 30 is provided between the pair of rollers 10 and 20 and a motor 30 for driving these rollers.
Since the drive switching means 40 for selectively transmitting the driving force from the roller 10 to only one of the rollers 10 and 20 is provided, the following operation and effect can be obtained. That is, when the recording material is relatively slippery ordinary paper, the driving force from the motor 30 is transmitted by the drive switching means 40 only to the pressure roller 20, which is a relatively hard roller, and is driven. (The fixing roller 10, which is a relatively soft roller, is driven by the pressure roller 20). Since the pressure roller 20 has a small amount of thermal deformation, a change in radius due to a temperature difference is small. Therefore, when the pressure roller 20 is driven, the conveyance speed of the recording material by the fixing device is also hardly affected by the temperature change, and the conveyance speed difference between the conveyance speed of the recording material by the transfer unit is also reduced. Therefore, even if the recording material is relatively long paper, the recording material is unlikely to be pulled between the fixing device and the transfer portion or to be largely slackened. Defects are less likely to occur in the image formed thereon.

On the other hand, when the recording material is a relatively slippery synthetic resin sheet or the like, the driving force from the motor 30 is transmitted by the drive switching means 40 only to the fixing roller 10 which is a relatively soft roller. This can be driven (the pressure roller 20, which is a relatively hard roller, follows the fixing roller 10). When the relatively soft fixing roller 10 is driven, slippage between the recording material and the rollers 10 and 20 is less likely to occur, and slip marks are less likely to occur on the image. The slip is less likely to occur because the relatively soft roller 10 is driven and the recording medium is compared with the case where the relatively hard roller 20 is driven and the relatively soft roller 10 is driven through the recording material. Hard roller 20
This is because a smaller frictional force is required between the rollers 10 and 20 and the recording material in the case where is driven.
As described above, when the fixing roller 10, which is a relatively soft roller, is driven, the conveyance speed of the recording material by the fixing device greatly varies due to a change in temperature, and the conveyance speed of the recording material by the transfer unit is changed. In particular, when the recording material is relatively long paper, the recording material may be pulled between the fixing device and the transfer unit, or the recording material may be largely sagged. However, recording materials that are relatively slippery, such as synthetic resin sheets, are usually short, so that the above-mentioned problems are unlikely to occur.

As described above, according to the image forming apparatus of this embodiment, by switching the driving roller according to the type of the recording material, the recording material is relatively slippery when the recording material is a normal paper. A good image can be formed in any case where the image is relatively slippery.

<Second Embodiment> FIG. 2 is a schematic perspective view showing a fixing device in an image forming apparatus according to a second embodiment of the present invention. In the figure, the same or corresponding parts as in the first embodiment are denoted by the same reference numerals.

This embodiment differs from the first embodiment in that a pair of rollers 10 and 20 are pressed against each other via a heated fixing belt 50, and are different from the other embodiments. There is no.

The fixing belt 50 is stretched between the fixing roller 10 and the heating roller 60 and circulates following the fixing roller 10 and / or the pressure roller 20.

The heating roller 60 is formed of a material having excellent thermal conductivity (eg, aluminum) in a pipe shape.
A heat source (not shown) is disposed therein. The heating roller 60 can rapidly heat the fixing belt 50 at a portion where the fixing belt 50 is wound. The heating roller 60 of this embodiment is configured as a tension roller, and is urged in the tension direction of the fixing belt 50 by an appropriate urging means (not shown).

According to the image forming apparatus of this embodiment,
The pair of rollers 10 and 20 are fixed to the fixing belt 50 to be heated.
, The recording material onto which the toner image has been transferred at the transfer unit passes through a pressure contact portion N1 between the fixing belt 50 of the fixing device and the pressure roller 20 pressed against the surface 51 of the fixing belt. Thereby, the toner image is fixed on the recording material. Since the fixing belt 50 has a smaller heat capacity than the rollers, the initial heating time can be reduced.

As described above, in the configuration in which the pair of rollers 10 and 20 are pressed against each other via the fixing belt 50, if the configuration is such that the pressure roller 20 which is a relatively hard roller is driven, as described above. As described above, when the recording material is relatively slippery, the slip easily occurs on the front and back of the recording material. However, according to the image forming apparatus of this embodiment, the recording material is relatively slippery. In this case, the driving force from the motor 30 is transmitted to only the fixing roller 10 which is a relatively soft roller by the drive switching means 40, and the fixing roller 10 can be driven (the fixing belt 50).
And the pressure roller 20 is driven by the fixing roller 10), so that by driving the fixing roller 10, slipping between the recording material, the roller, and the fixing belt is less likely to occur, and slip marks are less likely to occur on the image. That is,
The configuration described in the first embodiment, in which the drive rollers are switched according to the type of the recording material, is particularly effective when the pair of rollers 10 and 20 are pressed against each other via the fixing belt 50.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and can be appropriately modified within the scope of the present invention.

[0030]

According to any one of the image forming apparatuses according to the first and second aspects, by switching the driving roller according to the type of the recording material, the recording material is relatively slippery when the recording material is relatively slippery. A good image can be formed in any case where the image is relatively slippery. Further, according to the image forming apparatus of the second aspect, it is possible to shorten the initial heating time until fixing can be performed.

[0031]

[Brief description of the drawings]

FIG. 1 is a diagram showing a fixing device according to a first embodiment of an image forming apparatus according to the present invention, wherein FIG.
(B) and (c) are operation explanatory diagrams.

FIG. 2 is a schematic perspective view showing a fixing device in a second embodiment of the image forming apparatus according to the present invention.

FIG. 3 is a schematic diagram illustrating a transfer unit and a fixing unit in a general image forming apparatus.

[Explanation of symbols]

 S Recording material 1 Transfer unit 2 Fixing unit N Pressure contact unit 10 Fixing roller (relatively soft roller) 20 Pressure roller 30 Motor (drive source) 40 Drive switching means 41, 42 Electromagnetic clutch 50 Fixing belt

Claims (2)

[Claims] 1. A transfer section for transferring a toner image onto a recording material, and a pair of rollers having different hardnesses are pressed against each other, and a roller formed in a convex shape on a relatively soft roller side when viewed from the axial direction of the roller. An image forming apparatus comprising: a fixing unit that fixes a toner image on a recording material through a recording material onto which the toner image has been transferred, at a pressure contact portion between the pair of rollers, and drives the pair of rollers; An image forming apparatus, comprising: a drive switching unit configured to selectively transmit a driving force from a driving source to only one of the rollers. 2. The apparatus according to claim 1, wherein said pair of rollers are in pressure contact with each other via a heated fixing belt.
The image forming apparatus as described in the above.