JP3368155B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a method for forming a visible image (toner image) on an image carrier by an electrophotographic recording method or an electrostatic recording method, and the like. The present invention relates to a full-color or mono-color image forming apparatus such as a copying machine or a printer, which transfers an image to a transfer material to obtain an image. 2. Description of the Related Art An image forming apparatus employing an electrophotographic recording method forms a latent image on a photosensitive drum as an image carrier using light, magnetism, electric charge, and the like, and develops the latent image. An image forming unit that visualizes the toner image as a toner image, a transfer material conveying unit that conveys the transfer material to a transfer position of the image forming unit, and a fixing unit that fixes the toner image on the transfer material onto which the toner image has been transferred at the transfer position And As the transfer material transporting means, a belt-like transporting member, that is, a transfer material transporting belt is used from the viewpoint of transportability, and an image forming section of each color is formed on the transporting belt along the belt. You. A transfer material, for example, a recording sheet, is held on a conveyance belt by electrostatic attraction, and is sequentially conveyed to a transfer position of an image forming unit for each color and further to a fixing unit by rotation of the conveyance belt. [0006] The above-mentioned transport belt is stretched and supported by being wound around one driving roller and at least one driven roller, and is constituted as a transfer material transporting means which rotates endlessly. [0005] Between the driving roller and the driven roller, a conveyor belt is devised so as to be stretched with a constant force, and by arranging the driving roller downstream in the conveying direction, the conveying roller facing the image forming section is conveyed. The belt is devised so that it does not slack. A high friction material layer is formed on the outer periphery of the driving roller so that the driving force is transmitted to the conveyor belt without slipping. [0007] Thus, it is ensured that the transport belt moves at a constant speed from the most upstream image forming section to the most downstream image forming section. [0008] On the recording paper that is attracted and held on the transport belt and transported to the transfer position of each image forming unit, the toner image of each color formed on the image carrier of each image forming unit is sequentially placed. The image is superimposed and transferred. The paper on which the toner images of each color have been transferred is subjected to color mixing of the toner images of each color and fixing to the paper by heat (and pressure) in a fixing unit arranged close to the downstream side in the transport direction of the transport belt. A full-color print image is formed. In recent years, printers and copiers have been miniaturized, and the transfer / transport belt and the fixing unit have been arranged close to each other with a minimum gap. It has come to be. However, the above-described image forming apparatus has the following problems. That is, when the apparatus power is turned on, the heater of the fixing unit is automatically activated, and the temperature rises to a predetermined temperature. Part of the heat at this time is transmitted to the outside of the fixing unit, and as a result, the temperature inside the apparatus also rises to some extent. In particular, since the belt drive roller of the transfer / conveyance unit is located near the fixing unit, the amount of rise is larger than that of the other parts. As a result, the rollers expand and the transport speed of the transport belt changes. When the change in the transport speed exceeds a certain range, the transfer image appears as expansion and contraction. Further, in the case of an apparatus as shown in FIG. 3 in which different images from a plurality of image forming units are successively superimposed and transferred onto the same transfer material, there is a problem in transfer deviation of each image. Referring to the image forming apparatus shown in FIG. 3 , the apparatus is roughly divided into an image input section 90R and an image output section 90P. The image input section 90R inputs image information to be recorded, This is a device for sending the image signal to the image output unit 90P after performing the processing. The image output unit 90P includes an image forming unit 91a, 91b, 91c, 91d for forming a recording image, a paper feeding unit 92 for stacking recording paper P and sending it out one by one;
A transfer / conveyance unit 93 for transporting the recording paper P sent from the paper supply unit 92 to the image forming units 91a to 91d while transferring the image to the recording paper, and fixing the image recorded on the recording paper. And a control unit 95 for controlling all operations in these devices. When the operation of the apparatus is started, first, one sheet of recording paper P is fed from the paper feed unit 92 and sent to the registration roller 96 located in front of the transport unit 93. At this time, the registration roller 96 has stopped. Thereafter, the registration roller 96 rotates in synchronization with the image recording start signal, and sends out the recording paper P onto the transport unit 93. By this operation, an image can be formed at a predetermined position on the recording paper. The recording paper P sent from the registration rollers 96 is transported to a plurality of image transfer areas Ta, Tb, Tc, Td while being held on a transport unit 93, and images from the image forming sections 91a to 91d are transferred. It is transferred and recorded on the surface. When recording on the recording paper P is performed, the transport unit 93 transports the recording paper P to the vicinity of the fixing unit 94, and
The recording paper is fed to the fixing unit 94 while separating the leading end. Then, heat (and pressure) is applied to, for example, a fixing roller nip portion of the fixing unit 94 to fix the toner image on the recording paper. Thereafter, the recording paper P is discharged outside the apparatus via a paper discharge unit. [0017] Particularly in the case of the image forming apparatus shown in FIG. 3,
Although depending on the path length between the image forming units, a problem occurs even if the speed changes by about 0.1%. The belt driving roller 97 has a structure in which a layer having a high coefficient of friction (high friction layer), for example, a rubber layer is wound at least 1 mm or more in thickness on the roller surface in order to drive the belt without slipping. It is common. However, those substances generally have a large coefficient of linear expansion. Then, usually, the expansion amount cannot often be ignored as an image shift. In concrete terms, the thickness of the rubber layer is 2 m
In the case of m, the diameter increases by about 0.1% (in other words, the speed increases by 0.1%) when the roller temperature rises by about 20 degrees. Therefore, in order to avoid this problem caused by the fixing unit, a method of arranging a heat insulating material around the fixing unit so as to prevent heat dissipation as much as possible may be implemented. However, the area where the transfer material enters or exits must be left open, and escape from the area cannot be prevented. Also, considering the space and cost for the use of the heat insulating material, it is not always the best measure. Further, it is conceivable to keep the minimum necessary heater operation, such as by not attaching the fixing heater, except during the operation of the apparatus. However, it is necessary to wait for the user to temporarily raise the fixing temperature to a predetermined value for each operation of the apparatus. And the usability deteriorates. Accordingly, an object of the present invention is to provide an image forming apparatus which has a simple structure without extra space and cost, and which does not cause expansion and contraction of a transferred image and transfer deviation of a multiplex image due to the temperature in the apparatus. That is. The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
At least one image carrier on which an image is formed, an endlessly rotating conveyance belt for holding and conveying a transfer material for transferring a toner image on the image carrier, and a conveyance belt downstream in the conveyance direction of the conveyance belt. And at least one driving roller that supports and drives the transport belt, at least one driven roller that stretches while supporting the transport belt, and is disposed adjacent to and downstream of the drive roller in the transport direction; A fixing unit for fixing the toner image to the transfer material by heat, wherein the drive roller has a hollow structure in the axial direction, and is provided near one shaft end of the drive roller.
And a fan for generating an airflow toward the one shaft end.
And a fan inside the hollow structure.
And the airflow from one shaft end to the other shaft end
The image forming apparatus is characterized in that the drive roller is generated to cool the drive roller . Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings. First Embodiment First, a first embodiment of the present invention will be specifically described with reference to FIGS. Hereinafter, an image forming method is an electrophotographic method, and a color image output apparatus in which a plurality of image forming units considered to be particularly effective for the present invention will be described in parallel. The image forming apparatus shown in FIG.
R and an image output unit 1P. The image output unit 1P is roughly divided into an image forming unit 10 (four stations Pa,
Pb, Pc, and Pd are provided side by side and have the same configuration), a paper feed unit 20, a transfer / conveyance unit 30, a fixing unit 40, and a control unit (not shown). Further, each unit will be described in detail. The image forming unit 10 has the following configuration. Note that the station Pa will be described as an example. A photosensitive drum 11a is supported at its center as an image carrier, and is driven to rotate in the direction of the arrow. The primary charger 12a and the optical system 13 face the outer peripheral surface of the photosensitive drum 11a in the rotation direction thereof.
a, a developing device 14a is disposed. In the primary charger 12a, the photosensitive drum 11
A uniform amount of charge is given to the surface of a. Next, a light beam such as a laser beam modulated according to a recording image signal is exposed on the photosensitive drum 11a by the optical system 13a, thereby forming an electrostatic latent image thereon. Further, the electrostatic latent image is visualized by the developing device 14. In this apparatus, four color developers such as yellow, cyan, magenta, and black (hereinafter, referred to as developer)
These are referred to as toners).
4b, 14c, and 14d, which are arranged close to the photosensitive drums 11a to 11d of the stations Pa to Pd. On the downstream side of the image transfer area Ta in the rotation direction of the photosensitive drum, the cleaning device 15a cleans the surface of the drum by scraping off the toner remaining on the photosensitive drum 11a without being transferred onto the recording paper P. According to the process described above, image formation using each toner is sequentially performed at the stations Pb, Pc, and Pd. The paper feeding unit 20 includes a cassette 21 for storing the recording paper P, a pickup roller 22 for feeding out the recording paper one by one from the cassette, and a registration roller 25A for feeding the recording paper P sent from the pickup roller 22. , A paper feed roller 23a for conveying up to 25B,
23b, the paper feed guide 24, and the transfer / transfer unit 3 for transferring the recording paper P in accordance with the image forming timing of the image forming unit.
0, and a suction guide 26 for guiding the recording paper P to the transfer / conveyance unit 30. The transfer transport unit 30 will be described in detail. The recording paper holding sheet 31 (made of PET (polyethylene terephthalate) or PVdF (polyvinylidene fluoride) is used as the material) around a plurality of rollers, that is, the belt driving roller 32, the driven roller 33, and the tension roller 34. Thus, the transfer belt 31 is formed. Then, an image transfer plane A is formed between the belt driving roller 32 and the driven roller 33. More specifically, the distance between the transfer belt and the photosensitive drum is very small (about 1 mm).
is seperated. The belt drive roller 32 has a surface of a metal roller coated with rubber (urethane or chloropsin) having a thickness of several mm to prevent slippage with the belt. The belt drive roller 32 is driven by a pulse motor 39. As will be described later, the rotation speed can be easily changed. The tension roller 34 is a holding sheet (hereinafter, referred to as a holding sheet).
This is a roller for applying an appropriate tension to the transfer belt 31. An adsorbing charger 27 is disposed at a position where the recording paper P sent from the registration rollers 25A and 25B enters the transfer belt 31, and each of the photosensitive drums 14a to 14 downstream thereof is disposed.
In the image transfer areas Ta to Td where the transfer belt and the transfer belt oppose each other, a transfer charging blade 35 a
To 35d are arranged. These charging blades 35
Reference numerals a to 35d denote photosensitive drums 14a to 14d by a mechanism (not shown).
14d can be pressurized and separated, and at the time of pressurization, good image transfer is performed by lifting the transfer belt 31 and pressing it against the photosensitive drums 14a to 14d with an appropriate pressure. A charging / discharging charger 36 for separating and removing the recording paper is disposed slightly upstream of the transfer driving roller 32, and a charging / discharging charger 37 for applying a uniform charge to the surface of the transfer belt 31 is provided downstream thereof. A brush roller 38 for cleaning the recording paper holding surface of the transfer belt 31 is provided. The fixing unit 40 includes a fixing roller 41A having a heat source such as a halogen heater therein, a pressure roller 41B pressed against the roller (this roller may also be provided with a heat source), and the roller pair. And an inner discharge roller 44 and an outer discharge roller 45 for further guiding the recording paper discharged from the pair of rollers to the outside of the apparatus. . Here, the distance between the fixing roller 41A and the transport driving roller 32 is about 100 mm or less. The control unit includes a control board 50 and a motor drive board 51 for controlling the operation of the mechanism in each unit. Next, description will be made in accordance with the operation of the apparatus.
When the image forming operation start signal is issued, first, the recording paper P is sent out from the cassette 21 one by one by the pickup roller 22. Then, the paper is guided between the paper feed guides 24 by the paper feed rollers 23a and 23b, and is conveyed to the registration rollers 25A and 25B. At this time, the registration rollers 25A and 25B are stopped, and the leading end of the paper strikes the nip. Then, the registration rollers 25A, 2
5B starts rotating at the timing when the image forming section starts forming an image. The rotation timing is set so that the recording paper and the toner image on the photosensitive drum exactly coincide in the image transfer area. When the recording paper P enters the transfer belt 31 being moved by the transfer drive roller 32 and comes into contact therewith, it is electrostatically attracted by the Coulomb force generated on the transfer belt 31 by the action of the attraction charger 27. The transfer belt 31 rotates in synchronization with the photosensitive drums 11a to 11d, and the recording paper P is conveyed to the first image transfer area Ta while being held thereon. There, a high voltage is applied to the transfer charging blade 35a pressurized at the start of the sequence in accordance with the passage timing of the recording paper P. Then, the toner image formed on the photosensitive drum 11a by the above-described process is transferred onto the surface of the recording paper P, and is further conveyed to the next image transfer areas Tb to Td. In this case, the image formation is performed by delaying only the time required for the recording paper to be transported between the stations, and the next toner image is transferred by registering the registration on the previous image. The following station P
The above steps are similarly repeated for b, Pc, and Pd.
Multiple color toner images are transferred. When the multiple transfer is completed, the adsorbing force between the recording sheet and the transfer belt is reduced by the operation of the charge removing charger 36 in the separation section, and the recording sheet is separated from the transfer belt 31 by the subsequent curvature of the transfer drive roller 32. I do. The recording paper separated from the transfer belt 31 is accurately guided to the fixing roller nip by the entrance guide 43. The toner image is fixed on the recording paper surface by the heat of the roller pair 41A and 41B and the pressure of the nip. Thereafter, the recording paper is conveyed by the inner and outer discharge rollers 44 and 45, and the recording paper is discharged outside the apparatus. The transfer blade 35 is released from the pressure, and the sequence ends with the transfer belt 31 separated from the photosensitive drum. This is to protect the photosensitive drum by preventing external force from acting on the photosensitive drum as much as possible. Next, the characteristic features of the present invention in this embodiment will be described below. The belt driving roller 32 shown in FIG. 2 is composed of a metal core 320 and a rubber layer 321 of several mm wound on the surface thereof. The core 320 has a through hole 322 therein. It is provided with a hollow structure. An axial fan 325 is arranged near the shaft end 324 so that air flows into the through hole 322 from one shaft end 323 of the belt driving roller 32 and is discharged from the other shaft end 324. The air is acting in the suction direction. The axial fan may be configured to blow air into the through hole 322 near the shaft end 323. Further, both ends 32 of the belt driving roller 32
Areas 3 and 324 are open to the outside of the image forming apparatus. As described above, the outside air flows through the through hole 322 of the belt driving roller 32 by the action of the axial fan 325, so that the belt driving roller 32
Can be kept constant. Therefore, according to the present embodiment, the temperature of the belt driving roller is kept constant without being influenced by the heat radiated from the fixing unit, so that the belt speed does not change and the transfer image expands and contracts, Can be prevented from occurring. As is apparent from the above description, according to the present invention, the transport belt is The rotating drive roller has a hollow structure in the axial direction and is arranged near one shaft end of the drive roller.
And a fan that generates an airflow toward the one shaft end.
The fan has a fan inside the hollow structure.
To generate airflow from one shaft end to the other shaft end.
The drive roller is configured to cool, so it is possible to prevent the expansion and contraction of the transfer image and the transfer misalignment of the multiplex image due to the effect of the temperature inside the device with a simple structure without extra space and cost, and always High quality images can be maintained. [0063]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram illustrating an example of a full-color image forming apparatus in which the present invention is embodied. FIG. 2 is a configuration diagram illustrating a driving roller and a cooling unit according to the first embodiment. FIG. 3 is a schematic configuration diagram illustrating an example of a conventional image forming apparatus. DESCRIPTION OF SYMBOLS 11 Photosensitive drum (image carrier) 32 Drive roller 33 Follower roller 40 Fixing unit 322 Through-hole (hollow) 323, 324 Shaft end 325 Axial fan (cooling means)

Claims (1)

(57) An endless rotation for holding and conveying at least one image carrier on which an image is formed and a transfer material for transferring a toner image on the image carrier. A transport belt, at least one drive roller positioned downstream of the transport belt in the transport direction and supporting and driving the transport belt; and at least one driven roller extending and supporting the transport belt. wherein is arranged close to the conveying direction downstream of the drive roller, in an image forming apparatus and a fixing unit for fixing the toner image to the transfer material by heat, wherein the drive roller is a hollow structure in the axial direction, the drive The roller is disposed near one shaft end of the roller.
A fan that generates an airflow toward one of the shaft ends, and the fan causes the one side inside the hollow structure.
To generate airflow from the shaft end to the other shaft end,
An image forming apparatus, wherein the drive roller is cooled .