JP2003107815A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paper carrying path and a paper carrying means by which transfer deviation is not generated in a device transferring an image on a photoreceptor to recording paper in the paper carrying path. SOLUTION: In the apparatus, the distance from a nip position between a pair of resist rollers installed on an upstream side of a transfer part and a nip position between a pair of fixing rollers installed on a downstream side of the transfer part is set to be shorter than the length in the carrying direction of a minimum size recording paper sheet that can be used. Furthermore, the relationship between circumferential speed Vr of the pair of resist rollers, circumferential speed Vd of the photoreceptor and circumferential speed Vt of the pair of fixing rollers is set to be Vd>Vt>Vr.

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 for transferring a toner image on a photoconductor, which is an electrostatic latent image carrier, onto recording paper.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, a photosensitive drum is rotated at a constant speed, and an image forming unit having processes such as charging, exposing, and developing is used to form a photosensitive member. A toner image is formed by the charged toner on the body surface. Further, in order to transfer the toner image formed on the surface of the photoconductor onto the recording paper, a paper conveying unit that conveys the recording paper from the registration roller pair to the image forming unit, and the paper conveying unit conveys the toner image to contact the surface of the photoconductor. Transfer means for transferring the toner image onto the recording paper,
There is provided a fixing unit that causes the toner image transferred on the recording paper to pass through a fixing roller pair including a heat roller and a pressure roller to fix the toner image on the recording paper.

In recent years, with the increase in the number of devices having a copying function and a printer function due to digitalization and the demand for downsizing of the devices and improvement of operability, the paper storage portion, the image forming means, and the fixing means are arranged vertically. Therefore, an increasing number of apparatuses are configured to form an image on a conveyance path whose length extending in the vertical direction is shortened.

[0004]

One of the important factors for obtaining good image quality in the image forming apparatus having the above structure is the transfer process. In order to accurately transfer the toner image on the surface of the photoconductor onto the recording paper to obtain a good image, it is necessary to bring the recording paper into contact with the surface of the photoconductor while moving at the same peripheral speed. The movement of the recording paper in the transfer unit is affected by the conveying force of the conveying unit, the pulling force of the fixing unit, the conveying force of electrostatically adsorbing the surface of the photoconductor and the recording sheet, and in some cases A deviation from the surface of the photoconductor causes an image defect called a so-called transfer deviation. In particular, when the leading edge and the trailing edge of the sheet pass through the roller pair, the transfer deviation is likely to occur due to the impact due to the collision, the return of the bending of the recording sheet, and the fogging due to the rigidity of the recording sheet.
In addition, when the transport path is shortened, the transport unit and the fixing unit come close to the transfer unit, and there is a problem that an image defect is likely to occur under the influence of them.

[0005]

In view of the above problems, the present invention aims to transfer a toner image formed on a surface of a photoconductor in an image forming portion of an image forming apparatus onto a recording paper in a good condition. To aim.

According to a first aspect of the present invention, an image forming means for forming a toner image by the toner charged on the surface of the photosensitive drum which is rotationally driven at a constant speed, and a recording paper directed toward the image forming portion to a pair of registration rollers. And a transfer unit that transfers the toner image formed on the surface of the photoconductor onto a recording sheet, and the recording sheet on which the toner image is transferred is passed through a fixing roller pair to fix the toner image. In an image forming apparatus having a fixing unit, a paper transport path length from the nip position of the registration roller pair to the nip position of the fixing roller pair is set shorter than a length of a recording paper size to be used in the transport direction. The peripheral speed of the fixing roller pair is set to be slightly higher than the peripheral speed of the registration roller pair, and the peripheral speed of the photosensitive drum in the previous term is the peripheral speed of the fixing roller pair in the previous term. It is characterized in that remote is set further slightly faster.

As a result, the recording paper is conveyed to the surface of the photosensitive drum by the registration roller pair at a constant speed and electrostatically adsorbed to the surface of the photosensitive drum. At this time, since the surface of the photosensitive drum is slightly faster than the peripheral speed of the pair of registration rollers, the recording paper is conveyed in a state in which a tensile force is applied. The recording paper is conveyed to the fixing means by the registration roller pair and the photosensitive drum, and is nipped and conveyed to the fixing roller pair of the fixing means. Here, when the recording paper passes through the nip portion of the registration roller pair, the recording paper is bent due to the tensile force due to the conveying force of the photosensitive drum, and the rear end is separated from the registration roller pair. At this time, it is possible to prevent the transfer deviation from occurring due to the return of the bending. Further, since the peripheral speed of the pair of fixing rollers is slightly lower than the peripheral speed of the surface of the photosensitive drum, the recording paper is not pulled from the surface of the photosensitive drum. This prevents the occurrence of transfer deviation due to the influence of the fixing unit.

According to a second aspect of the present invention, in the transfer means of this image forming apparatus, the transfer roller to which a charge having a polarity opposite to that of the toner is applied is opposed to the photosensitive drum with a minute gap. The transfer roller is arranged so as to be driven to rotate at the same peripheral speed as the photosensitive drum.

The transfer means is structurally classified into a corotron system in which charging is performed by using corona discharge without directly contacting the recording paper, and a rubber roller (transfer roller) rotating at the same peripheral speed as the surface of the photoconductor. There is a transfer roller system in which an electric charge is applied to contact the back surface of the recording paper to charge it. The transfer roller method includes a contact method in which the transfer roller is pressed into contact with the surface of the photoconductor when it is subdivided, and a non-contact method in which a minute gap about the thickness of the recording paper is provided between the surface of the transfer roller and the surface of the photoconductor. . The transfer roller system has advantages that it does not generate ozone, and that it has a high performance of transporting recording paper in close contact with the photosensitive drum. The contact method has an advantage that the recording paper is nipped and conveyed by the photosensitive drum and the transfer roller,
There are problems that the transfer roller is contaminated with toner, the contact affects the wear of the photoconductor drum, and the unevenness in the driving of the transfer roller easily affects the rotation of the photoconductor drum, which causes image unevenness. The non-contact type transfer roller according to the second aspect solves these problems, makes it possible to appropriately bring the recording paper into close contact with the photosensitive drum, and convey the recording paper at the peripheral speed of the photosensitive drum. .

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below by taking a copying apparatus as an example. The following embodiments and examples are examples of embodying the present invention and do not limit the technical scope of the present invention.

FIG. 1 shows a schematic sectional view of a copying apparatus which is one of the embodiments of the present invention. In the copying machine 1, a base frame 2 is arranged at the lowermost portion to support the entire apparatus, and a paper storage unit 1 for stacking and storing recording paper inside thereof.
0 is supported so that it can be pulled out forward. An image forming frame 3 formed of a resin material and having a substantially L-shaped cross section is fixed onto the base frame 2. An image forming unit 11, which can be attached / detached from the front of the apparatus, is positioned and fixed in the left space in the image forming frame 3. The image forming unit 11 includes a charging unit 21 around the photoconductor drum 20,
An exposure unit 22, a developing unit 23, and a cleaning unit 24 are provided. Further, the image forming frame 3 is provided with a sheet conveying unit 12 having a transfer device 16 on the left side facing the image forming unit 11, and further the conveying unit 1 is provided.
The fixing device 13 is attached above the image forming unit 11 and the image forming unit 11. A laser unit 14 for exposing an image to laser light on the surface of the charged photosensitive drum 20 is attached to the right space in the image forming frame 3. In addition, a paper discharge unit 15 for stacking recording sheets on which images are formed is formed in the external space above it. An image reading device 5 for irradiating a document placed on a contact glass or a document conveyed on a reading unit to read image information and convert it into an electric signal is fixed to the upper surface of the image forming frame 3, On the upper part of the image reading device 5, a document pressing member and a document pressing device 6 having a function of automatically conveying a sheet document are placed.

In the copying machine 1, the toner image formed on the surface of the photosensitive drum by the image forming unit is transferred to the paper storage unit 10.
An image is formed by transferring the image onto a recording sheet fed from and fixing it by the fixing device 13. Therefore, the paper storage unit 1
A paper transport path 7 for transporting recording paper from 0 to the paper discharge unit 15 is formed. The sheet conveyance path 7 extends from the sheet storage section 10 to the fixing device 13 in a substantially vertical direction, is curved to the right on the downstream side thereof, and extends to a sheet discharge section 7 in a substantially horizontal direction. Further, a half-moon-shaped paper feed roller 30 is provided above the left side of the paper storage unit 10 as a recording paper conveyance means, and a registration roller pair 31 is arranged near the entrance of the paper conveyance path 7. A discharge roller pair 33 is provided at the most downstream portion. Further, although not shown, on the rear side of the apparatus, driving means for rotationally driving the image forming unit 11, the fixing device 13, the recording sheet conveying means, and the like, and a high-voltage power supply to the image forming unit 11 are supplied. There are provided a high-voltage board for controlling, a control board for controlling the operation of electronic components in the apparatus, and the like.

Next, the conveyance of the recording paper will be described in more detail. FIG. 2 is a cross-sectional view showing in detail the configuration of the paper transport path 7 of the copying apparatus 1. The recording paper P is stacked on the mounting plate 10a on the left side in the paper storage unit 10, and is biased upward by the springs 10c with both end corners regulated by the claws 10b so that the uppermost surface is always at a constant height. Is maintained. The sheet feeding roller 30 includes a half-moon shaped rubber roller portion 30.
a and a notch 30b are formed. Further, a spring clutch mechanism is provided on the rotary shaft, and the cutout portion 30b is controlled so as to be held in a stopped state at a position facing the recording paper P or to rotate clockwise. The cutout portion 30b is at a position retracted from the upper surface of the recording paper P, but when the paper feed roller rotates, the rubber roller portion 30a contacts the upper surface of the recording paper P, and a frictional force acts on the uppermost recording paper P. The paper is removed from the claws and sent to the paper transport path 7. As for the circumferential length of the rubber roller portion 30a of the paper feed roller 30, the leading end of the recording paper P is the paper transport path 7
Has a length longer than the moving distance to reach the nip portion of the pair of registration rollers 31 arranged near the entrance of the sheet, and rotates once to feed one sheet of paper.

The pair of registration rollers 31 arranged near the entrance of the sheet conveying path 7 is a roller in which one roller 31a is formed by POM, and an electromagnetic clutch is provided on the rotating shaft to stop and rotate the roller at any timing. It can be switched. The other roller 31b is made of CR rubber and is biased and supported by the roller 31a.
It is configured to rotate at the same peripheral speed following the rotation of.
The paper detection switch 3 is provided near the upstream side of the registration roller 31.
2 are arranged. The paper detection switch 32 can always detect the presence / absence of paper on the conveyance path, and can detect the passage of the leading edge and the trailing edge of the recording paper P. The rotation of the registration roller pair 31 is started after a predetermined time from the timing when the leading edge of the fed recording paper is detected by the paper detection switch 32. At that time, the leading edge of the recording paper is the registration roller pair 31.
The time is set to be slightly longer than the time predicted to come into contact with the nip portion of the. Further, the formation of the toner image on the photosensitive drum is also controlled based on the detection timing of the paper detection switch 32.

A part of the photosensitive drum 20 in the circumferential direction is exposed in the sheet conveying path 7 on the downstream side of the pair of registration rollers 31, and the transfer device 16 is arranged in the sheet conveying unit 12 so as to face it. ing. Here, the transfer device 16 will be described with reference to FIGS. FIG. 3 is a perspective view of the outer shape of the paper transport unit 12 as viewed from the direction facing the inside of the apparatus. FIG. 4 is a diagram illustrating the configuration of the transfer unit 16. The paper transport unit 12 is provided in the paper transport path 7 from near the entrance to between the fixing device 13, the outside is a part of the exterior of the left side of the device, and the guide faces 12a and 12b and the resist are inside. One roller 31a of the roller pair and the transfer means 20 are provided. Further, the paper transport unit 12 is rotatably supported by a fulcrum 12c provided on the image forming frame 3 below, and a hook 12d provided above engages with an engaging portion of the image forming frame 3, A conveyance path is formed so as to face the image forming unit 11. When the hook 12d is disengaged and the transport unit 12 is opened outward, the area from the entrance of the paper transport path 7 to the fixing unit 13 is exposed.

The transfer device 16 is provided with a transfer roller 40 in which a rubber roller portion 40a made of urethane foam is formed on a metal shaft core 40b. As shown in FIG. 4A, in the transfer roller 40, the shaft cores 40 b on both sides have the bearing 4
The bearing 41 is rotatably held by 1. The bearing 41 is swingably supported by the paper transport unit 12 and is biased toward the photosensitive drum by the biasing means 42. Positioning rollers 43 are inserted in the shaft cores 40b on both sides. The positioning roller 43 is a polyacetal (P
OM) is a molded product using a resin material such as a shaft core 40
It is rotatably inserted into b without any play. The outer diameter of the positioning roller 43 is precisely formed to a size slightly larger than the outer diameter of the transfer roller, and contacts the surface of the photoconductor drum outside the image forming area to expose the transfer roller 40 to the surface of the rubber roller portion 40a. It is held at a position where a minute gap is formed on the surface of the body drum. A drive input gear 44 that engages with the shaft core 40b and integrally rotates is attached to the outside of the positioning roller 43 on one shaft core 40b. Figure 4
As shown in (c), a positioning guide 45 in which a groove having the same width as the diameter of the shaft core 40b is formed in a substantially horizontal direction is provided in a part of the housing near both ends in the front-rear direction of the image forming unit 11. Has been. The vicinity of the tips of the shaft cores 40b on both sides is inserted into the positioning guide 45 to regulate the vertical position, and the transfer roller 40 is positioned parallel to the shaft center of the photosensitive drum 20. Further, as shown in FIG. 4B, the pre-transfer guide 46 is urged by the biasing means 47 with the shaft center 40b of the transfer roller 40 as a fulcrum.
It is rotatably supported while being biased toward.
The pre-transfer guide member is a member formed of a resin material,
The protrusions 46a are provided over the entire width in the transport direction, and the protrusions 46a formed near both ends contact the housing of the image forming unit 11 for positioning in the rotational direction.

In the fixing device 13, a heat roller 13a provided with a halogen lamp 13c as a heat source inside a metal cylindrical member, and a roller portion made of a rubber material pressed against the heat roller 13a are formed. Pressure roller 13
b. The surface temperature of the heat roller 13a is provided at one location on the peripheral surface and is detected by a temperature sensor (not shown), and the lighting of the halogen lamp 13c is controlled so as to maintain a constant set temperature. Further, a drive gear is attached to one end side and is rotationally driven at a constant speed. The pressure roller 13b is rotatably supported via a bearing and is rotated by the rotation of the heat roller 13a.

Next, the conveyance control for preventing the transfer deviation in the sheet conveyance path 7 relating to the present invention will be described again with reference to FIG. The copying apparatus 1 of the embodiment can form an image on a maximum size A4 size recording paper, and can form an image on a minimum size A5 size paper. The dashed-dotted line in the paper transport path 7 in FIG. 2 is the transport trajectory of the paper predicted for general recording paper. In the transport path of the sheet transport path 7, the distance L from the nip portion of the registration roller pair 31 to the nip portion of the roller pair of the fixing device 13 is about 140.
mm. This is the length l in the transport direction of A5 size recording paper, which is the minimum size for image formation.
The distance is shorter than (about 148 mm). Therefore, when the trailing edge of the recording paper leaves the nip portion of the registration roller pair, the leading end side reaches the nip portion between the heat roller 13a and the pressure roller 13b. That is, when the recording paper is conveyed without being transferred by the photoconductor drum 20 and the transfer roller 40, at least the upstream side of the transfer portion of the recording paper is in the conveying state by the registration roller pair 31, or the downstream side is conveyed. The pair of rollers of the fixing device 13 is in the transporting state. With such a configuration, the sheet is not conveyed only by the transfer portion of the photoconductor drum, and thus it is possible to prevent the transfer deviation caused by the conveyance failure due to the insufficient conveyance force.

Next, the peripheral speeds of the registration roller pair 31, the photosensitive drum 20, and the fixing device 13 will be described. The photosensitive drum 20 has a diameter of about 30 mm and a peripheral speed Vd of about 1
It is rotationally driven at 10 mm / sec. On the other hand, the peripheral speed Vr of the registration roller pair 31 is 0.
The speed is set to about 3% slower. Also, the fixing device 1
The peripheral speed Vt of the roller pair of No. 3 is set to a speed slower by about 0.15% than Vd. Therefore, the relationship between the three peripheral speeds is Vd>Vt> Vr. As a result, in the situation where the recording paper extends over both the registration roller pair 31 and the transfer portion of the photoconductor drum 20, tension due to the conveyance force of the photoconductor drum 20 and the transfer roller 40 acts on the recording paper between them. ing. Therefore, the sheet is not bent between the transfer portion and the registration roller pair, and when the rear end of the transfer recording sheet is separated from the registration roller pair 31, the transfer deviation is caused by vibration when the bending of the recording sheet is extended. It becomes possible to prevent. The speed difference between Vd, Vr, and Vt is set to about 0.3% to 0.15% because the outer diameter of the photosensitive drum 20, the outer diameters of the rollers 31a and 31b of the transfer roller pair 31, and the heat This is to prevent the speed difference between Vt and Vr and Vd and Vt from being reversed in the range of the error in consideration of the error in each dimension of the outer shape of the roller 13a. Further, since the conveyance force of the registration roller pair 31 is stronger than the conveyance force of the photoconductor drum 20 and the transfer roller 40, the speed difference between the two becomes a slight slip between the surface of the photoconductor drum and the recording paper. When the speed difference is increased, there arises a problem that the equal magnification of the transferred image in the carrying direction is out of the reference range.
It is desirable to keep the speed difference of r to 0.5% or less.

Next, the state of the recording paper between the transfer portion of the photosensitive drum 20 and the fixing device 13 will be described. The discharging direction of the recording paper from the transfer portion is set to a direction in which a slight angle is swung away from the photosensitive drum for the purpose of separating the recording paper electrostatically attracted to the surface of the photosensitive drum 20. There is. Further, a plurality of separation claws are provided in the axial direction so as to contact the surface of the photosensitive drum on the downstream side of the transfer section. The guide surface 12b of the sheet conveying path 7 from the transfer portion to the fixing device 13 on the side having the transfer device is a concave surface gently curved with respect to the straight line connecting the transfer portion, the nip position of the heat roller and the pressure roller. . The recording paper ejected from the transfer section may be guided by the guide surface 12b depending on the rigidity and the charged state of the recording paper.
It is expected that there will be changes such as when traveling along the road or on the other side. Paper transport path 7 that changes depending on the recording paper
Due to the locus in (1), the speed difference between Vt and Vd causes the recording paper to bend or a slight slip occurs in the transfer portion. Here, when the rear side of the recording paper is on the registration roller pair 31, it is assumed that tension acts on the recording paper between the transfer unit and the fixing device due to the speed difference between Vt and Vr. Since the occurrence of bending of the recording paper between the transfer section and the transfer portion is reliably prevented, the transfer deviation when the trailing edge of the recording paper leaves the registration roller pair is surely prevented. Further, after the trailing edge of the recording paper passes through the registration roller pair 31, the fixing device 1
Since the peripheral speed Vt of 3 is set to be lower than the peripheral speed Vd of the photoconductor drum 20, it is possible to prevent the transfer deviation from being caused by being pulled by the fixing device 13.

[0021]

As described above, by using the configuration of the sheet conveying path of the present invention and the setting of the peripheral speeds of the photosensitive drum, the pair of registration rollers, and the fixing device, the electrostatic capacity having a relatively short conveying path can be obtained. Even in the image forming apparatus using the recording method, it is possible to surely prevent image defects such as transfer deviation occurring in the transfer portion.

[Brief description of drawings]

FIG. 1 is a sectional view showing an outline of a copying apparatus using the present invention.

FIG. 2 is a cross-sectional view showing details of a sheet conveyance path of the copying apparatus shown in FIG.

FIG. 3 is a perspective view showing the outer appearance of a transport unit that constitutes a part of a sheet transport path in the copying apparatus shown in FIG.

4 is an explanatory diagram illustrating a transfer unit of the copying apparatus shown in FIG.

[Explanation of symbols]

1 Copier 7 Paper transport path 11 Imaging unit 12 Transport unit 13 Fixing means 13a heat roller 13b pressure roller 16 Transfer device 20 photoconductor drum 30 paper feed rollers 31 Registration roller pair 40 transfer roller

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ryoji Kanamatsu             1-22 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka Prefecture             Kyocera Mita Co., Ltd. (72) Inventor Toshiyuki Nakamura             1-22 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka Prefecture             Kyocera Mita Co., Ltd. (72) Inventor Junya Yoda             1-22 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka Prefecture             Kyocera Mita Co., Ltd. F term (reference) 2H027 ED02 ED17 ED25 EE01 EE03                       ZA10                 2H033 AA14 AA21 BA02 BA08 BA11                       BB17 BB37 CA36 CA40                 2H071 CA01 CA02 CA05 DA09 DA12                       DA15 DA22 DA23 EA04                 2H072 AB07 BA03 BB01 CA01 CB07                       CB08 JA02                 2H200 FA04 FA20 GA23 GA29 GA34                       GB25 GB30 HA11 HB12 HB23                       JA02 JA29 JB10 LA15 PA11

Claims (2)

[Claims] 1. An image forming means for forming a toner image by a charged toner on the surface of a photosensitive drum which is rotationally driven at a constant speed, and a conveying means for conveying a recording sheet toward a pair of registration rollers toward the image forming portion. Image formation having transfer means for transferring the toner image formed on the surface of the photoconductor onto recording paper, and fixing means for passing the recording paper on which the toner image has been transferred through a pair of fixing rollers to fix the toner image. In the apparatus, the paper conveyance path length from the nip position of the registration rollers to the nip position of the fixing roller pair is set to be shorter than the length of the recording paper size to be used in the conveyance direction. The speed is set to be slightly higher than the peripheral speed of the registration roller pair, and the peripheral speed of the photoconductor drum is set to be slightly higher than the peripheral speed of the fixing roller pair in the previous period. The image forming apparatus according to claim 1, characterized in Rukoto. 2. A transfer roller, to which a charge having a polarity opposite to that of the toner is applied to the photosensitive drum, is arranged to face the photosensitive drum so as to have a minute gap, and the transfer roller and the photosensitive drum are opposed to each other. The image forming apparatus according to claim 1, wherein the image forming apparatus is rotationally driven at the same peripheral speed.