JP2003337489A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a fixing device for securing stable image quality by preventing the irregularity of image and transfer shift that are liable to occur in a belt type fixing device. <P>SOLUTION: This image forming apparatus having a belt type fixing device for applying pressure on a fixing belt and a transfer material with a belt supporting roller disposed at an inner side of the fixing belt and a pressing roller installed at an outer side of the fixing belt across the heated fixing belt and fixing toner on the transfer material, is provided with a length adjustment mechanism for varying the length of a sub pressure area in the advancing direction of the transfer material, wherein a main pressure area at a nip part and the sub pressure area at the upstream or downstream of the main pressure area are formed, and a center distance regulating mechanism for maintaining a center distance constant between the belt supporting roller and the pressing roller which forms the main pressure area when the transfer material is heated and pressed. <P>COPYRIGHT: (C)2004,JPO

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 copying machine or a printer having a belt type fixing device.

[0002]

2. Description of the Related Art A toner image surface side is oriented so that it faces the surface of an endless fixing belt maintained in a predetermined temperature range.
A transfer material that holds an unfixed toner image is fed, and the transfer material is pressed against the fixing belt by a belt support roller and a pressure roller that are opposed to each other with the fixing belt sandwiched between the fixing belt and the belt support roller. roller,
A copying machine configured to fix the toner image on a transfer material through heating and pressing action of a pressure roller.
An image forming apparatus using an electrophotographic system such as a printer has been generalized as a publicly known.

However, the fixing device using the fixing belt has a drawback as described with reference to FIG.

FIG. 8 is a view showing the arrangement of a belt supporting roller, a fixing belt, a pressure roller and a heating roller of the fixing device.

In the figure, the belt support roller covered with an elastic layer and the pressure roller press the fixing belt against each other with a pressure spring so that the belt support roller elastically deforms to form a main pressure area a. The fixing process is performed in the main pressing area a near the roller contact surface of a straight line (normal line) A connecting the centers of the belt supporting roller and the pressing roller, which are arranged so as to face each other with the fixing belt interposed therebetween. As one means for improving the fixing performance and the fixing performance, the pressure roller is displaced in the D direction against the tension of the fixing belt to move the pressure roller and the belt supporting roller into a nip portion (hereinafter referred to as a main pressing member). A method of increasing the sub-pressure area b, which is a winding area where the fixing belt and the pressure roller contact each other except the pressure area a), is performed.

However, according to this method, although the sub-pressurizing area b which is the winding amount surely increases, the drag force of the fixing belt which pushes back the pressure roller acts in the arrow direction,
The pressure roller is moved away from the belt support roller, and the position where the main pressure area a becomes small is indicated by the dotted line (position of normal line A1).
When the belt speed fluctuates according to the load change (deformation amount of the elastic layer) in the main pressure area a, and the problems such as the slack of the paper and the image rubbing due to contact with the fixing belt occur. There is.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides an image forming apparatus capable of forming a stable image without image rubbing or transfer deviation by a simple device. With the goal.

[0008]

[Means for Solving the Problems] A heated fixing belt is sandwiched and a pressure is applied to the fixing belt and a transfer material by a belt supporting roller inside the fixing belt and a pressure roller installed outside the fixing belt to transfer the toner. In an image forming apparatus having a belt-type fixing device for fixing toner on a material, a main pressure area at a nip portion and a sub pressure area upstream or downstream of the main pressure area are formed. A shaft having a length adjusting mechanism for varying the length of the pressure region and for maintaining a constant axial distance between the pressure roller and the belt supporting roller forming the main pressure region when the transfer material is heated and pressed. An image forming apparatus having an inter-distance defining mechanism.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION First, an image forming apparatus of the present invention will be described.

In the description of the embodiments of the present invention, the technical scope of the present invention is not limited by the terms used in this specification.

FIG. 1 is a schematic diagram showing an example of the overall configuration of the image forming apparatus. In the figure, 10 is a photoconductor, 11 is a scorotron charger which is a charging unit, 12 is a writing device which is an image writing unit, 13 is a developing unit which is a developing unit, and 14 is cleaning for cleaning the surface of the photoconductor 10. An apparatus, 15 is a cleaning blade, 16 is a developing sleeve, and 20 is an intermediate transfer belt. Image forming means 1
Is a photoconductor 10, a scorotron charger 11, a developing device 13,
Since the image forming means 1 for each color has the same mechanical structure, the reference numeral is attached only to the structure of the Y (yellow) series, and M (magenta). , C (cyan) and K
The reference symbols are omitted for the components in (black).

The arrangement of the image forming means 1 for each color is in the order of Y, M, C, and K with respect to the running direction of the intermediate transfer belt 20, and each photoconductor 10 is a stretched surface of the intermediate transfer belt 20. And is rotated at the contact point in the same direction as the running direction of the intermediate transfer belt 20 and at the same linear velocity.

The intermediate transfer belt 20 includes a driving roller 21, a ground roller 22, a tension roller 23, and a charge eliminating roller 2.
7. The belt unit 3 is stretched around the driven roller 24, and these rollers, the intermediate transfer belt 20, the transfer device 25, the cleaning device 28 and the like constitute the belt unit 3.

The traveling of the intermediate transfer belt 20 is performed by the rotation of the drive roller 21 by a drive motor (not shown).

The photoconductor 10 is formed by forming a conductive layer, an a-Si layer, or a photosensitive layer such as an organic photoconductor (OPC) on the outer periphery of a cylindrical metal substrate formed of, for example, an aluminum material. Rotate in the counterclockwise direction indicated by the arrow in the figure with the grounded.

An electric signal corresponding to the image data from the reading device 80 is converted into an optical signal by the image forming laser, and the writing device 12 projects the light signal onto the photoconductor 10.

The developing device 13 is made of a cylindrical non-magnetic stainless steel or aluminum material which keeps a predetermined distance from the peripheral surface of the photoconductor 10 and rotates in the same direction at the position closest to the rotation direction of the photoconductor 10. The developing sleeve 16 is provided.

The intermediate transfer belt 20 has a volume resistivity of 10 ⁶
It is an endless belt of -10 ¹² Ω · cm and has a thickness of 0.1 with a conductive material dispersed in engineering plastics such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, and nylon alloy. A seamless belt having a two-layer structure, in which a semi-conductive film substrate having a thickness of ˜1.0 mm is coated with fluorine having a thickness of 5 to 50 μm, preferably as a toner filming prevention layer, is provided. In addition to this, a semi-conductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber or urethane rubber can be used as the base of the belt.

A transfer device 25 has a function of transferring a toner image formed on the photoconductor 10 onto the intermediate transfer belt 20 by applying a direct current having a polarity opposite to that of the toner. Transfer device 2
As 5, a transfer roller can be used in addition to the corona discharger.

Reference numeral 26 denotes a transfer roller which can be released from contact with the earth roller 22 and retransfers the toner image formed on the intermediate transfer belt 20 onto the transfer material P.

A cleaning device 28 is provided so as to face the driven roller 24 with the intermediate transfer belt 20 interposed therebetween. After transferring the toner image to the transfer material P, the intermediate transfer belt 20
The charge of the residual toner is weakened by the static elimination roller 27 to which an AC voltage having a DC voltage of the same polarity or the opposite polarity of the toner is applied, and the cleaning blade 29 cleans the toner remaining on the peripheral surface.

A fixing device 4 includes a fixing belt 40 formed by molding a metal base and silicon rubber into a belt shape, a belt supporting roller 41 for supporting and conveying the fixing belt 40, a heating roller 42, the fixing belt 40 and the transfer material P. The heating roller 42 is composed of a pressure roller 43 for pressing and heating and fixing with sandwiching the sheet, a belt cleaning web (not shown), and the like. The fixing belt 40, which has a halogen heater 47 for heating and is closely wound on the outer surface, is heated by its conductive heat. The temperature is detected by the contact temperature sensor 48 installed on the heating roller 42, and the temperature is controlled by the controller B1. The heating roller 42 is slidable in the arrow F direction by a spring 421 (see FIG. 3) via a bearing (not shown), and applies tension to the fixing belt 40.

The belt support roller 41 has a cylindrical core metal 410 (see FIG. 3) made of iron and a silicone-based elastic layer 411 (see FIG. 3) which is an elastic body, baked on the core metal 410 (not shown). It receives power from the main body drive device and rotates in the clockwise direction shown in the figure. Therefore, the drive transmission path is
(1) main body side drive source, (2) belt support roller 41,
(3) The fixing belt 40 and (4) the heating roller 42.

Reference numeral 70 is a paper feeding roller, 71 is a timing roller, 72 is a paper cassette, and 73 is a conveying roller.

Next, problems in the structure of the conventional belt type fixing device will be described. FIG. 2 is a diagram showing the amount of deformation of the elastic layer of the belt supporting roller by the pressure roller.

In the figure, the belt support roller 41 and the pressure roller 43 are pressed against each other by the pressure spring 425, and the belt support roller 41 is elastically deformed. If the thickness of the elastic layer 411 other than the main pressurizing region a is t1 and the main pressurizing region a is deformed to t2, the elastic layer 411 will be swept in a narrow gap in the arrow direction in the crushed state, In the main pressurization region a, when the deformation amount is smaller than the reference (thickness t2 is larger than the reference), the flow velocity is small, and conversely, when the deformation amount is large, the velocity is high.

If the sub-pressurizing area b is enlarged by displacing the pressure roller 43 in the D direction, the fixing belt 4
Considering a structure in which a force is exerted in the direction in which the pressure is returned to 0 and the main pressure area a is reduced, assuming that the reference transfer material conveyance speed is adjusted when the sub pressure area b is small, the sub pressure is applied. When the region b becomes large, the fixing conveyance speed becomes relatively small, and the transfer material is largely deflected in the conveyance path 49 (see FIG. 3) and comes into contact with the fixing belt 40, the guide member 45 of the conveyance path 49, or the like to prevent image rubbing. Will be awakened. On the contrary, when the sub-pressurization area b becomes small, the conveyance speed of fixing becomes high and the transfer material is pulled, so that the transfer deviation occurs in the transfer area S.

An object of the present invention is to prevent image rubbing and transfer deviation caused by the above causes.

FIG. 3 is a schematic view showing a cross section of the belt type fixing device of the present invention. In the figure, in the configuration of the present fixing device, the rotation shaft 4 of the pressure roller 43 and the belt support roller 41 is
The rocking lever 4 having a prescribed axial distance that rotates coaxially with the belt support roller 41 in order to keep the axial distances 34, 414 constant.
31 is provided, and the amount of deformation of the roller elastic layer 411 is always constant, and as a result, the main pressing area is kept constant. Incidentally, the swing lever 431 supports the pressure roller 43 via a heat insulating sleeve 432 (see FIG. 4).

In the above structure, in order to increase the gloss of the toner on the transfer material, it is necessary to lengthen the contact distance (contact time) of the transfer material P with the fixing belt 40. For that purpose, a length adjusting mechanism is provided which can shift the pressure roller 43 in the direction of the arrow H or the like to change the length of the sub-pressure area. That is, the cam 43 locked to the cam shaft 436
By rotating 5 it is possible to increase the sub-pressure area b. However, when the wrapping angle is increased, the path of the fixing belt 40 changes, so that the heating roller 42 moves in the direction opposite to F, the spring 421 is stretched, and the tension applied to the fixing belt 40 increases, and the pressure roller concerned. The force to push back 43 becomes strong, and the force acts in the direction in which the fixing pressure by the belt support roller 41 and the pressure roller 43 becomes small. However, the axial distance between the belt support roller 41 and the pressure roller 43 becomes Since it is kept constant by the swing lever 431 which is an inter-axis distance regulating mechanism, the fixing conveyance speed is kept constant.

FIG. 4 is a cross-sectional view of the pressure roller and the pressure portion of the belt support roller. In the figure, the belt support roller 4
1 is supported by a fixing device frame body (hereinafter, simply referred to as a frame body) 50 via heat insulating sleeves 413 at both ends. The pressure roller 43 is supported by the swing lever 431 at both ends via the heat insulating sleeve 432, and the swing lever 43 is supported by the swing lever 43.
1 is coaxially supported by the belt support roller 41, and maintains a constant pressure (elastic deformation) by maintaining a predetermined axial distance from the pressure roller 43. As described above, in order to change the sub pressure area b, when the cam 435 of the length adjusting mechanism is rotated by a predetermined angle, the rocking lever 431 is rotated and moved about the belt support roller 41,
By this movement, the width of the sub pressure area b between the pressure roller 43 and the fixing belt 40 can be changed.

In the present invention, since the pressure roller 43 is supported by the swing lever 431, the cam 435 causes the pressure roller 43 to move the pressure roller 43 through the swing lever 431.
Even if the sub-pressurization region b is enlarged by pressure bonding to the 0 side, the axial distance is constant, so that the deformation amount of the elastic layer 411 is constant.
Regardless of the wrapping angle of the fixing belt 40 around the pressure roller 43, a constant fixing pressure, that is, a constant fixing conveyance speed can be obtained.

Further, another embodiment is shown in FIGS. FIG. 5 is a diagram showing a pressure roller and a pressure portion of the belt support roller by means of the spacer between shafts.

FIG. 6 is a sectional view showing a mechanism for regulating the axial distance between the pressure roller and the belt supporting roller.

In FIGS. 5 and 6, the pressure roller 43 is supported by the swing lever 431 via a heat insulating sleeve 432.
The heat insulating sleeve 432 can slide in the arrow direction along the groove 424 provided in the swing lever 431. Also,
The swing lever 431 rotates coaxially with the rotation shaft 414 of the belt support roller 41. The rotation shafts 414 and 434 of the belt support roller 41 and the pressure roller 43 are spring-loaded 42.
The pressure spring 422 is hooked through the rollers 1, 423, and the contact surfaces of both rollers are elastically deformed by pressing, but since the inter-shaft spacer 420 is provided on the rotating shaft 414 side,
As long as the pushing back of the tension of the fixing belt 40 is smaller than the applied pressure, the amount of deformation of the elastic layer 411 is determined by the distance between the shafts by the spacers 420, so the pressure roller 43 of the fixing belt 40.
A constant fixing pressure, that is, a constant fixing conveyance speed can be obtained regardless of the wrap angle.

In this embodiment, the inter-shaft spacer is provided on the rotation shaft side of the belt support roller 41, but it is provided not on the rotation shaft side of the belt support roller 41 but on the rotation shaft side of the pressure roller 43. Also, even if the inter-axis spacers are provided on both the shafts, it is possible to have a configuration in which a constant inter-axis distance is maintained. Further, in the present embodiment, the pressure roller 43 is moved by the swing lever 431 coaxially supported by the belt support roller 41, but in addition to this, the shaft of the pressure roller 43 is slid along the guide. Of course, it is possible to apply various mechanisms such as moving by a link.

Usually, since the fixing load is 100 to 700 N and the fixing belt tension is about 10 to 60 N, the axial distance can be kept constant even in the axial spacer method. Even outside this range, if the fixing load (the tensile load of the pressure spring 422) is larger than the force of the fixing belt 40 to push back the pressure roller 43, the same effect is exhibited. To do.

As described above, according to the present invention, since the axial distance between the pressure roller 43 and the belt supporting roller 41 can be kept constant, the speed of the fixing belt 40 does not change and the image rubbing and the image shift can be prevented.

Further, it is possible to avoid image fluctuation and image shift due to speed variation due to hardness change of the elastic layer 411 and speed variation due to insufficient processing accuracy.

Although FIG. 7 is a schematic view of the fixing device having a structure in which the sub-pressurizing area is located downstream of the main pressurizing area, the sub-pressurizing area b is located upstream of the main pressurizing area a. Since the same thing can be said as the relationship between the fixing belt 40 and the pressure roller 43, the description thereof will be omitted.

Next, the image forming process will be described with reference to FIG. Simultaneously with the start of image recording, the photoconductor 10 of the color signal Y is rotated in the counterclockwise direction by the start of a photoconductor drive motor (not shown), and at the same time, a potential is applied to the photoconductor 10 by the charging action of the scorotron charger 11. Is started.

After a potential is applied to the photoconductor 10, the writing device 12 starts writing an image corresponding to the Y image data, and the surface of the photoconductor 10 is printed with Y of the original image.
An electrostatic latent image corresponding to the image is formed.

The electrostatic latent image is reversely developed by the Y developing device 13 in a non-contact state, and Y is developed according to the rotation of the photoconductor 10.
Toner image is formed on the photoconductor 10.

The Y toner image formed on the photoconductor 10 is transferred to the intermediate transfer belt 2 by the action of the Y transfer device 25.
0 is transcribed.

Thereafter, the photoconductor 10 is cleaned by the cleaning device 14 and the next image forming cycle is started (the same applies to the M, C and K cleaning processes, so the description thereof is omitted).

Next, the writing device 12 writes an image corresponding to the M (magenta) color signal, that is, the image data of M, and the M of the original image is printed on the surface of the photoconductor 10.
An electrostatic latent image corresponding to the image is formed. The electrostatic latent image becomes an M toner image on the photoconductor 10 by the M developing device 13, and the intermediate transfer belt 20 is transferred to the M transfer device 25.
It is synchronized with the Y toner image above and is superimposed on the Y toner image.

By a similar process, the toner image of C (cyan) is synchronized with the superimposed toner images of Y and M, and the toner image of C (cyan) is transferred onto the superimposed toner image of Y and M by the transfer device 25 of C. The toner images of K (black) are superposed and synchronized with the superposed toner images of Y, M, and C.
In the K transfer device 25, the superimposed toner images of Y, M, and C are superimposed, and the superimposed toner images of Y, M, C, and K are formed on the intermediate transfer belt 20.

The intermediate transfer belt 20 carrying the superposed toner image is sent in the clockwise direction as indicated by the arrow, and the transfer material P is sent out from the paper cassette 72 by the paper sending roller 70, and passes through the carrying roller 73, The transfer roller 26 is conveyed to the timing roller 71 and driven by the timing roller 71 so as to be synchronized with the superimposed toner image on the intermediate transfer belt 20 and to which a DC voltage having a polarity opposite to that of the toner is applied (intermediate transfer roller 26). The superposed toner image on the intermediate transfer belt 20 is transferred to the transfer material P by being fed to the transfer area S (which is in contact with the belt 20).

After that, the intermediate transfer belt 20 runs, the charge of the residual toner is weakened by the charge eliminating roller 27, and the intermediate transfer belt 20 is cleaned by the cleaning blade 29 which is in contact with the intermediate transfer belt 20, and the next image forming cycle is started.

Transfer material P on which the superimposed toner images have been transferred
Is further sent to the fixing device 4, and is sandwiched between the belt support roller 41 and the pressure roller 43 via the fixing belt 40, and is pressed and fixed. The transfer material P on which the toner image is melted and fixed is conveyed to the paper discharge tray 82 by the paper discharge roller 81.

[0051]

By keeping the axial distance between the pressure roller and the belt supporting roller constant, it is possible to prevent the fixing conveyance speed from fluctuating, and avoid image rubbing and transfer deviation due to the conveyance speed fluctuation.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating an example of the overall configuration of an image forming apparatus.

FIG. 2 is a diagram showing a deformation amount of an elastic layer of a belt supporting roller by a pressure roller.

FIG. 3 is a schematic view showing a cross section of a belt type fixing device of the present invention.

FIG. 4 is a cross-sectional view of a pressure roller and a pressure portion of a belt support roller.

FIG. 5 is a view showing a pressure roller by a spacer between shafts and a pressure portion of a belt support roller.

FIG. 6 is a cross-sectional view showing a mechanism that regulates an axial distance between a pressure roller and a belt support roller.

FIG. 7 is a schematic view of a fixing device having a structure in which a sub pressure area is located downstream of the main pressure area.

FIG. 8 is a diagram showing an arrangement of a belt supporting roller, a fixing belt, a pressure roller, and a heating roller of a fixing device.

[Explanation of symbols]

1 Image forming means 3 Belt unit 4 fixing device 40 fixing belt 41 Belt support roller 43 Pressure roller 420 Spacer between shafts 422 pressure spring 431 Swing lever

Claims (2)

[Claims] 1. A toner on a transfer material is formed by sandwiching a heated fixing belt and applying pressure to the fixing belt and the transfer material by a belt supporting roller inside the fixing belt and a pressure roller installed outside the fixing belt. In an image forming apparatus having a belt-type fixing device for fixing a sheet, a main pressure area at the nip portion and a sub-pressure area upstream or downstream thereof are formed,
A shaft of the belt support roller and the pressure roller that has a length adjusting mechanism that varies the length of the sub-pressurizing region in the transfer material traveling direction, and that forms a main pressurizing region when the transfer material is heated and pressed. An image forming apparatus having an axial distance regulating mechanism that maintains a constant distance. 2. The image forming apparatus according to claim 1, wherein the sub-pressurizing area is constituted by the pressing roller and a belt wound around the pressing roller.