JP2003223060A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more surely suppress the occurrence of a defective image in a toner image transfer process by further improving an image forming device wherein a tension is applied onto a transfer material by making the speed of transporting the transfer material to a transfer part lower than the rotational circumferential speed of a transfer roller. <P>SOLUTION: A paper guide 9 constituted by making an upper guide 11 and a lower guide 10 face each other in the vertical direction is arranged between a pair of resist rollers 17 and a transfer device 4 (transfer part) in the undermentioned state. When a tangent drawn from the entrance point 22a of a transfer nip between a photoreceptor 3 and a transfer roller 4a to the lower guide is expressed with La, the tangent drawn from the transport nip exist point 19 of the pair of resist rollers to the lower guide is expressed with Lb, the tangent point of the tangent La with the lower guide is expressed with Pa, the tangent point of the tangent Lb with the lower guide is expressed with Pb, and an optional point on a paper sliding part on the lower guide surface is expressed with Pc, the mean radius of curvature of a circle decided by three points with namely the tangent point Pa, the tangent point Pb and the point Pc, is set to be ≥10 mm. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a laser printer,
More specifically, the present invention relates to a transport speed control technique in the relationship between a transfer device that sends a transfer material to a transfer portion and a transfer device.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, the transfer material conveying speed (hereinafter, simply referred to as "speed") in each portion of the electrophotographic image forming apparatus is set to an appropriate value. As a whole, the transfer material conveyance is balanced. In this case, the speed of the transfer material is controlled by appropriately setting the rotational peripheral speed of the transfer material conveying roller in each of the above-mentioned parts. In particular, the transfer material (hereinafter, also referred to as paper) in the paper feeding portion is a transfer portion (a portion for transferring the image formed on the image carrier to the transfer material) so as not to adversely affect the image formation. Transfer material transfer speed when sending to
Transfer material transfer speed in transfer device (transfer part transfer speed)
The roller rotation peripheral speed is set to be slightly faster than that, so that a slight bending (deflection) is created between both parts. By doing so, it is possible to prevent an image shift due to the pulling of the transfer materials, and a conveyance shake due to a large bending.

However, as described above, when the transport speed of the roller before transfer, that is, the speed of the transfer material moving from the paper feeding portion to the transfer portion is increased, bending is formed in front of the transfer portion, so that the transfer material is skewed in the longitudinal direction. May occur, image distortion and wrinkles on the transfer material may occur. Further, as a result of the paper being pushed to the transfer portion by the flexure, the transfer image expands and contracts, resulting in a magnification error before and after the image. Furthermore, when the transfer material is being fed, the transfer material (mechanism for conveying the transfer material to the transfer part) and the transfer part slip at the transfer part, so the actual transfer material speed is It will not be the same as the traveling speed of each device such as the transfer device or the transfer part that is sent to the set. In addition, the actual transfer material speed fluctuates and changes depending on the transfer material condition, the device usage condition, and the like.

In particular, since the image forming apparatus has been downsized and the distance between the transfer unit for feeding the transfer material to the transfer unit and the transfer unit has been shortened, it becomes difficult to control the speed by making the above-mentioned bending. There is. Therefore, for example, the following has been proposed as a transfer material speed control technique in the image forming apparatus.

In the invention of Japanese Unexamined Patent Publication No. 10-319658 (the title of the invention: an image forming apparatus), a transfer section for transferring an image formed on an image carrier to a transfer material, and an upstream side in the transport direction of the transfer section. In the image forming apparatus, the sheet feeding unit supplies the transfer material to the transfer unit, and the fixing unit located on the downstream side of the transfer unit in the transport direction and fixes the transfer material on which the image is transferred. A means for detecting the amount of bending of the paper is provided between the transporting means of the transfer section and the transporting means of the transfer section, and between the transporting means of the transfer section and the transporting means of the fixing section. Then, when the amount of flexure becomes equal to or greater than a predetermined value, control is performed so that the transport speed of the upstream-side transport unit during transport of the transfer material is slower than the transport speed of the downstream-side transport unit, and the amount of flexure becomes equal to or less than the predetermined value. When this happens, the transport speed of the upstream transport means during transport of the transfer material is made higher than the transport speed of the downstream transport means. Or keep the transport speed at the transfer section constant,
The transfer speed of the transfer material by the transfer means of the paper feed unit and the fixing unit is changed. By doing this, it is possible to form a high-quality image without blurring or rubbing of the image, without the need for highly accurate speed control, high precision of parts, and delicate adjustment, and keeping the amount of deflection of the transfer material appropriate. I am able to do it.

Further, in the invention of Japanese Unexamined Patent Publication No. 6-239489 (Title of Invention: Transfer Material Conveying Device), the transfer material conveying speed by the conveying means for transferring the transfer material to the transfer portion is set to the speed of the image carrier (rotating speed). Speed), and after a loop is formed at the leading edge of the transfer material, slow the speed of the transfer device that sends the transfer material to the transfer section to reduce the loop and generate tension in the transfer material. By deploying the means
The sudden generation of tension is eliminated to prevent the positional deviation of the transfer material, the image deviation, the image omission, and the occurrence of wrinkles.

On the other hand, regarding the transfer quality of the toner image onto the transfer material, image defects such as blurring and scattering pose a problem. Therefore, in the invention of Japanese Unexamined Patent Publication No. 6-3974 (title of the invention: image forming apparatus), the shape of the guide member for guiding the transfer material to the transfer portion is specified so that the distance between the transfer material and the image carrier is as small as possible. By conveying the transfer material while narrowing it, image defects are prevented.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the invention of 9658, a deflection detecting device is provided between the respective devices. However, such a bending detection device must be installed near the conveyance path, and the installation position thereof must be carefully considered. However, recently, because the image forming apparatus has become smaller and smaller, it is difficult to secure a place for installation. In addition, there are many inconveniences such as installation of hardware such as a photo sensor is costly, the number of parts is increased, and assembly position accuracy is required because it requires time and effort in the manufacturing process.

Further, in the invention of Japanese Patent Laid-Open No. 6-239489, the type and environment of the transfer material, and the condition of slippage at the conveying portion and the transfer portion are not taken into consideration regarding the occurrence of the loop. Therefore, when the number of loops is reduced, the tension applied to the transfer material may be too large, which may cause image shift and wrinkles.

In order to suppress the speed fluctuation of the transfer material between the paper feeding portion and the transfer portion to be small without using the above-mentioned sensor, the initial conveyance state is set appropriately and various conditions are set in advance. You must anticipate speed fluctuations.

Therefore, as a result of a study by the present inventor, the feeding speed of the transfer material is stabilized by lowering the speed at which the transfer material is fed to the transfer portion rather than the rotational peripheral speed of the transfer roller and imparting tension to the transfer material. I found the area to do. As a result, the speed of the transfer material at the transfer portion can be kept within a certain range, the magnification error of the transfer material in the sub-scanning direction can be minimized, and an image without skew or slip can be stably formed. Equipment provided. The inventor of the present invention also provided a method and a device relating to conveyance control for suppressing an elongation deviation of an image in one sheet of transfer material in this image forming apparatus (Japanese Patent Application No. 20-49).
00-349756).

However, tension is applied to the transfer material (tension is generated by slowing the conveying speed on the transfer device side).
When conveyed, the transfer material is pressed against the guide member located on the opposite side of the loop and slides. The following problems can be considered as problems caused by this. (1) By widening the space between the image carrier and the transfer material,
Image defects occur during transfer. (2) When the sliding portion with the guide is the end portion of the guide, the transfer material is handled and the bending tendency is strongly generated. (3) Paper dust frequently occurs. (4) Due to an increase in the triboelectric charge amount, transfer defects are likely to occur.

The present invention has been made in view of the above problems, and an object thereof is to impart tension to the transfer material by lowering the speed at which the transfer material is fed to the transfer portion, lower than the rotational peripheral speed of the transfer roller. This is to prevent the above-mentioned inconvenience in the image forming apparatus.

[0014]

The invention according to claim 1 is
A cylindrical photoconductor that forms a toner image, a writing unit that writes an electrostatic latent image on the photoconductor, a developing device that converts the electrostatic latent image on the photoconductor into a toner image, a photoconductor, and a transfer roller. A transfer device configured to electrostatically transfer the toner image on the photoconductor to the transfer material, a transfer material feeding unit that feeds the transfer material in the paper feeding portion toward the transfer device, and the transfer material. A transport device including a pair of registration rollers for transporting the transfer material from the feeding unit to the transfer portion of the transfer device, and a fixing device for transporting the transfer material from the transfer portion and fixing the toner image on the transfer material. An image forming apparatus, comprising: an upper guide and a lower guide, wherein the transfer material conveying speed of the conveying device is slightly slower than the transfer material conveying speed of the transfer portion to convey the transfer material while applying tension. Are made to face each other in the vertical direction. A paper guide is provided between the transfer device and the transfer section, and a tangent line drawn from the transfer nip entrance point between the photoconductor and the transfer roller to the lower guide is La, and the transfer guide nip exit point of the registration roller pair is the lower guide. Lb is the tangent line drawn to, and Pa is the tangent line La contact point with the lower guide.
When the contact point with the lower guide of b is Pb and an arbitrary point on the surface of the lower guide where the paper slides is Pc, the contact point P
The image forming apparatus is characterized in that an average radius of curvature of a circle determined by the three points a, the contact point Pb and the point Pc is set to 10 mm or more.

According to the second aspect of the invention, the angle θ formed by the tangent line La and the photoconductor radial line Ra passing through the entrance point of the transfer nip is 90 °.
The image forming apparatus according to claim 1, wherein:

According to the third aspect of the present invention, when the intersection point where the tangent line Ld drawn from the end portion of the upper guide to the lower guide to the lower guide intersects the surface of the photoreceptor is Pr, the photoreceptor radial line passing through the intersection Pr. The image forming apparatus according to claim 1, wherein an angle α formed by Rb and the tangent line Ld is 150 ° or less.

In the invention according to claim 4, the length of the tangent line La (the distance from the transfer nip entrance point to the contact point Pa with the lower guide) is set to the length of the tangent line Lb (the transfer nip exit point to the contact point with the lower guide). 4. The image forming apparatus according to claim 1, wherein the image forming apparatus is shorter than Pb.

The correspondence between the reference numerals in the above claims and the reference numerals in the drawings described later is as follows. Here, for convenience, the components of the image forming apparatus will be described with reference numerals. (A) A tangent line La drawn from the transfer nip entrance point 22a between the photoconductor 3 and the transfer roller 4a to the lower guide 10 corresponds to the reference numeral 20a in FIG. 2, and (b) a transport nip exit point 19 of the registration roller pair 17. Tangent Lb drawn from the bottom guide 10 to
Corresponds to reference numeral 21a in FIG. Also, (c) tangent line L
The contact Pa with the lower guide 10a corresponds to the reference numeral 20b in FIG. 2, and (d) the contact Pb between the tangent line Lb and the lower guide 10b.
Corresponds to reference numeral 21b in FIG. Further, (e) an arbitrary point P on the surface of the lower guide 10 on which the paper slides.
c is as shown in FIG. 2, and (f) the photoconductor radial line Ra passing through the transfer nip entrance point 22a is denoted by reference numeral 22 in FIG.
Corresponding to c, (g) a tangent line Ld drawn from the end of the upper guide 11 on the transfer portion side to the lower guide corresponds to reference numeral 23 in FIG. Further, (h) the intersection point where the tangent line Ld intersects the surface of the photoconductor 3 is as shown in FIG. 3, and (i) the photoconductor radial line Rb passing through the intersection point Pr corresponds to the reference numeral 24 in FIG. To do.

The invention according to claim 5 is characterized in that the portion of the lower guide surface on which the paper slides is formed of a metal member having a smooth surface (small surface roughness).
The image forming apparatus according to any one of 4 above.

The invention according to claim 6 is the image forming apparatus according to claim 5, wherein the metal member is grounded.

The invention according to claim 7 is the image forming apparatus according to claim 5 or 6, wherein a groove is formed in a portion of the metal member on the transfer device side.

According to an eighth aspect of the invention, the image forming apparatus according to any one of the first to fourth aspects is characterized in that a portion of the lower guide surface with which the sheet comes into contact is formed by an outer peripheral surface of the idle roller. Is.

The invention according to claim 9 is characterized in that an extension of a straight line connecting the end portion of the lower guide on the transfer portion side and the contact point Pa is located closer to the photosensitive member than the center of rotation of the transfer roller. Item 9. An image forming apparatus according to any one of items 1 to 8.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments and examples of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram schematically showing an image forming portion of an image forming apparatus to which the present invention is applied, and FIG. 2 is an explanatory diagram showing a main portion structure thereof. In FIG. 1, reference numeral 1 is a writing unit (writing device), reference numeral 3 is a photoconductor (image carrier), reference numeral 4 is a transfer device, and reference numeral 7
Is a developing device, reference numeral 12 is a paper feed tray (paper feed unit), reference numeral 1
Reference numeral 7 is a pair of registration rollers (paper conveying device), and reference numeral 18 is a fixing device.

The image forming section has a photosensitive member 3, and a transfer roller 4a, a charging roller 5 and a developing device 7 are arranged around the photosensitive member 3. The photoconductor 3 is a charging roller 5
Is given an electric charge and uniformly charged. The apparatus of the present embodiment is a so-called negative / positive developing system in which the photoconductor 3 is negatively charged and positive toner is used. The negatively charged photoconductor 3 is irradiated with laser light by the writing unit 1, the charging potential changes according to the intensity, and a potential distribution is formed according to the presence or absence of laser light irradiation and the amount thereof. The writing unit 1 is provided with a semiconductor laser 6 as a light source of the laser light 2, and the laser light emitted from the semiconductor laser 6 is applied to the surface of the photoconductor 3 through an optical system (not shown) including a rotary polygon mirror 8 (polygon mirror) and a lens. To do. By rotating the polygon mirror 8 at a constant speed by a motor, main scanning on the photoconductor 3 can be performed.
As for the data to be written, the image signal after the data processing is turned on / off by a laser beam. As a result, an electrostatic latent image is formed on the photoconductor 3.

In the developing device 7, the positive toner is mixed with the magnetic carrier on the developing roller 15, and the developing roller 1
It is carried on the photoconductor by the rotation of 5, and is moved onto the electrostatic latent image on the photoconductor by the electric field strength to form (develop) a toner image. The toner image formed on the photoconductor is carried to the nip portion (transfer portion) between the photoconductor and the transfer roller 4a and transferred to the transfer roller 4a.
Is transferred by. The transfer roller 4a has a thickness of 10 mm to 30 m as a resistance layer around the core metal that also functions as a rotational drive.
EPDM with open cell, open cell or smoothness at m
It is made by coating materials such as SBR, BR, and chloroprene rubber. The volume resistance of this resistance layer is 10 ⁷ Ωcm.
To 10 ¹⁰ Ωcm. Further, the surface of the transfer roller 4a is pressed against the surface of the photoconductor by a spring (not shown) or the like, and the transfer roller is rotated by transmitting a driving force from a photoconductor rotatably driven by a motor through a gear. It is like this.

On the other hand, the sheets 12a, which are the transfer material, stacked on the paper feed tray 12 are separated and conveyed one by one by the registration roller pair 17 via the paper feed roller (paper feed roller) 13, and the registration roller pair 17 is provided. Stop once at the position. Next, the toner image on the photoconductor is sent toward the transfer device 4 in synchronization so that the toner image is correctly positioned on the paper. A paper guide 9 for guiding the paper 12a is provided between the registration roller pair 17 and the transfer device 4. The paper guide 9 includes an upper guide 11 on the photoconductor side,
It comprises a lower guide 10 on the transfer roller 4a side.

The paper 12a is guided by the paper guide 9 and is sandwiched between the photoconductor 3 and the transfer roller 4a to enter the nip portion. Here, a current is supplied from the power source 14 to the transfer roller 4a, and the toner image on the photoconductor 3 is transferred onto the paper 12a. After that, the sheet exiting the transfer section (nip section) is sent to the fixing device 18, where the transferred toner image is fixed and an image is formed, and then the sheet is ejected to the outside of the image forming section.

Here, the rotational peripheral speed of the photosensitive member 3 is Vo, the rotational peripheral speed of the transfer roller 4a is Vt, and the registration roller pair 1 is
When the rotational peripheral speed of 7 is Vr, the sheet is conveyed under the condition of Vt> Vr. In addition, Vo and Vt may be set to have different speeds. By setting Vt> Vr, the paper is conveyed between the registration roller pair and the transfer portion in a state where tension is applied to the paper. For a sheet of paper, this tension increases toward the rear in the transport direction (however, the paper transport force by the transfer roller and the photoconductor is generally smaller than the paper transport force by the registration roller pair. Is a guideline for the upper limit of tension).

When Vt> Vr, the sheet is conveyed while sliding strongly on the lower guide 10 according to the tension. Figure 2 here
As shown in FIG. 3, the tangent line 20a from the transfer nip entrance point 22a of the photoconductor 3 and the transfer roller 4a to the lower guide 10 and the tangent line 21a from the transport nip exit point 19 of the registration roller pair 17 to the lower guide 10 are considered. Lower guide 10 of 20a
When the contact point with the contact is 20b and the contact point with the lower guide 10 of the tangent line 21a is 21b, the paper is contacted with these contact points 20b and 21b.
The lower guide 10 is conveyed along the surface shape of the lower guide 10. That is, the paper slides on the surface of the lower guide 10 between the contact 20b and the contact 21b. If this surface shape is an edge, the paper is handled and the curl becomes large, so it is desirable to reduce the curvature of the surface as much as possible. Therefore, in the example (Example 1), the contact 20b and the contact 2
When 1b and an arbitrary point Pc on the sliding surface are taken and the average radius of curvature determined by these three points is set to 10 mm or more, the curl tendency of the paper is reduced.

In another embodiment (embodiment 2), as shown in FIG.
In, the influence of the positional relationship between the lower guide 10 and the tangent line 22b on the surface of the photoconductor 3 passing through the transfer nip entrance point 22a was examined. As a result, the lower guide 10 is tangent 22
It was found that the image defect extremely occurred when it was positioned below so as not to intersect with b, and the image defect was prevented by intersecting the image on the contrary. That is, in order to stably form a high-quality image, it has been confirmed that it is desirable to set the angle θ between the tangent line 20a and the photoconductor radial line 22c passing through the transfer nip entrance point 22a to 90 ° or less.

In still another embodiment (Example 3), the following experiment was conducted. When the sliding portion of the lower guide 10 is close to the transfer portion side while satisfying the above conditions, and in the case of the paper guide shape as shown in FIG. 2 and when it is close to the registration roller pair side (not shown) The transfer images were compared with each other. As a result, the image quality was better in the case of FIG. This is because when the tangent line 20a is longer than the tangent line 21a, the distance between the paper and the photoconductor is likely to be unstable, and conversely, in the case of FIG. 2 where the tangent line 20a is shorter, the distance is shorter. It was found to be stable.

In yet another embodiment (Example 4),
As shown in FIG. 3, the end portion 11 of the upper guide 11 on the transfer portion side
When b was lowered as much as possible so that the paper could enter the nip portion in a straight line, an image defect might occur. It was found that this is because the end portion 11b is located below the tangent line 20a in FIG. 3, and this separates the sheet from the photoconductor, which reduces the effect of preventing image defects. However, if the end portion 11b is set too high, the impact force when the front end of the paper collides with the photoconductor becomes large, and image formation failure occurs during writing or development with laser light on the photoconductor.

The shape of the front end of the paper when the front end of the paper collides with the photoconductor is tangential line 2 drawn from the end 11b to the lower guide 10.
3 (FIG. 3). Therefore, in yet another embodiment (embodiment 5), when the position of the end portion 11b is changed, the condition for reducing the image formation failure due to the change of the contact angle of the sheet with the photoconductor is the tangent line 23. It is confirmed that the angle α (counterclockwise angle from the tangent line 23 to the photoconductor radial line 24) formed by the tangent line and the photoconductor radial line 24 passing through the point where the crosses the photoconductor 3 is 150 ° or less. It was

Further, when a general plastic member formed by molding is used as the lower guide 10, a large amount of paper dust is generated. In addition, the shape of the sliding portion was changed due to abrasion, and the curvature of the surface was increased, so that the curl of the sheet was regenerated. Therefore, as shown in FIG. 4 (Example 6),
When the sliding portion was replaced with the surface-polished metal member 30, abrasion was reduced and the amount of paper dust generated was reduced due to the reduction of the friction coefficient.

Further, in the image forming section of FIG. 2, the transfer image is deteriorated due to a change in electrical transfer conditions due to a side effect of frictional electrification caused by sliding of the paper on the paper guide.
Then, when the above-mentioned metal member 30 was brought into electrical contact (not shown) with the metal casing of the image forming apparatus or the ground of the electric circuit, the image deterioration due to the side effect was reduced. Therefore, in still another embodiment (Embodiment 7), when a groove 31 was provided in the portion of the metal member 30 on the transfer portion side as shown in FIG. 5, paper dust was collected in this groove. As a result, the inside of the image forming unit is less likely to be contaminated with paper dust.

In yet another embodiment (Embodiment 8), FIG.
As described above, the idle roller 40 was installed on the sliding portion of the lower guide 10. It has been confirmed that when the paper comes into contact with the roller 40, sliding on the lower guide 10 is eliminated, paper dust generation is significantly reduced, and the triboelectric charge amount is also reduced.

When the leading edge of the sheet has a downward curl, such as double-sided printing, the leading edge of the sheet does not reach the transfer portion smoothly, and in some cases, a sheet jam occurs. Therefore, in still another embodiment (Embodiment 9), as shown in FIG.
When the adjustment is performed by changing the position of the end portion 25 on the transfer portion side of 0, the extension of the straight line 26 connecting the contact 20b and the end portion 25 is above the rotation center 4b of the transfer roller 4a, that is, on the photoconductor 3 side. It has been found that the paper jam does not occur if it is located at.

[0039]

As is apparent from the above description, according to the present invention, the following effects can be obtained. According to the first aspect of the present invention, by limiting the average radius of curvature of the surface shape of the sliding portion on which the paper slides on the lower guide to 10 mm or more, it becomes difficult for the paper in a tense state to bend.

According to the second aspect of the present invention, since the paper is conveyed while approaching the photoconductor, the image defects that occur when the toner image is transferred are reduced.

According to the third aspect of the invention, the impact force is weakened by reducing the contact angle when the leading edge of the sheet collides with the photoconductor. Therefore, deterioration during image formation due to the impact force is reduced. According to the invention of claim 4, the curving of the sheet comes closer to the transfer side, so that the distance between the sheet and the photosensitive member becomes stable, and thus image defects are reduced.

According to the fifth aspect of the present invention, the coefficient of friction when the paper slides on the surface of the lower guide is reduced, so that the change in the surface shape of the guide due to abrasion is reduced and the generation of paper dust is reduced. As a result, it is possible to prevent the effect of the invention of claim 1 from being deteriorated over time due to the change in the surface shape.

According to the invention of claim 6, the amount of frictional charge of the paper is reduced, and a good image can be obtained without changing the transfer conditions. According to the seventh aspect of the present invention, the paper dust collects in the groove on the downstream side of the sliding portion for the paper, and the stain due to the paper dust inside the image device is reduced. According to the invention of claim 8, the paper is guided to travel without sliding on the lower guide surface, so that the amount of paper dust generated and the amount of triboelectricity are reduced.

According to the ninth aspect of the invention, the problem that the contact angle between the front end of the paper and the transfer roller becomes steep due to the curving tendency of the front end of the paper is eliminated, and the paper jam is reduced.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram illustrating a configuration of an image forming unit of an image forming apparatus according to the present invention.

FIG. 2 is an image forming portion of FIG. 1, particularly Examples 1 to 3 of the present invention.
FIG. 3 is a schematic explanatory diagram showing a main configuration of an image forming unit according to the present invention.

FIG. 3 is a schematic explanatory diagram illustrating a main configuration of an image forming unit according to a fourth embodiment of the present invention.

FIG. 4 is a schematic explanatory view showing a main part of a lower guide according to a sixth embodiment of the present invention.

FIG. 5 is a schematic explanatory view showing a main part of a lower guide according to a seventh embodiment of the present invention.

FIG. 6 is a schematic explanatory view showing a main part of a lower guide according to an eighth embodiment of the present invention.

FIG. 7 is a schematic explanatory diagram illustrating a main part configuration of an image forming unit according to a ninth embodiment of the present invention.

[Explanation of symbols]

1 Writing unit (writing device) 2 laser light 3 photoconductor (image carrier) 4 Transfer device 4a Transfer roller 4b Rotation center 5 charging roller 6 Semiconductor laser 7 Developing device 8 Polygon mirror (rotary polygon mirror) 9 Paper guide 10 Lower guide 11 Upper guide 11b Transfer end side end 12 Paper tray (paper feeder) 12a Paper (transfer material) 13 Paper feed rollers 14 power supply 15 Developing roller 17 Registration roller pair (conveying device) 18 Fixing device 19 Transport nip exit point 20a tangent 20b contact 21a tangent 21b contact 22a Transfer nip entry point 22b tangent 22c Radius line of photoconductor 23 tangent 24 photoconductor radius line 25 End on the transfer side 26 straight line 30 metal members 31 groove 40 Idol Roller Vo Rotating peripheral speed of photoconductor Vr Rotating peripheral speed of registration roller pair Vt Rotational peripheral speed of transfer roller

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/14 G03G 21/00 372 F term (reference) 2H027 DA17 DA20 EA18 ED02 ED16 EE03 2H200 FA17 GA23 GA34 GA44 GB25 HA02 HB12 JA02 JB20 JB45 LA06 LA15 LC03 MA04 PA11 3F049 DA11 DA12 EA13 LA01 LB03 3F101 FB04 FC11 FD01 LA02 LA07 LB03

Claims (9)

[Claims] 1. A cylindrical photosensitive member for forming a toner image,
A writing unit for writing an electrostatic latent image on the photoconductor, a developing device for converting the electrostatic latent image on the photoconductor into a toner image, a photoconductor and a transfer roller are provided, and the toner image on the photoconductor is formed. A transfer device that electrostatically transfers the transfer material to the transfer material, a transfer material feeding means that feeds the transfer material of the paper feed unit toward the transfer device, and a transfer material from the transfer material feeding means to the transfer device. A transfer device including a pair of registration rollers for transferring the transfer material to the sheet transfer unit, and a fixing device that transfers the transfer material from the transfer unit and fixes the toner image on the transfer material, and transfers the transfer material transfer speed of the transfer device. An image forming apparatus configured to convey a transfer material while applying tension to the transfer material by making the transfer material transfer speed slightly lower than that of the other part, and a paper guide configured by vertically opposing an upper guide and a lower guide to each other. The transfer device and transfer unit The tangent line drawn from the transfer nip entrance point between the photoconductor and the transfer roller to the lower guide is La, the tangent line drawn from the transfer nip exit point of the registration roller pair to the lower guide is Lb, and the tangent line La is The contact with the lower guide is Pa, and the contact with the lower guide of the tangent line Lb is P
b, where Pc is an arbitrary point on the surface of the lower guide on which the paper slides, the contact point Pa, the contact point Pb, and the point Pc
An image forming apparatus characterized in that an average radius of curvature of a circle determined by the three points is 10 mm or more. 2. The image forming apparatus according to claim 1, wherein an angle θ formed by the tangent line La and a photoconductor radial line Ra passing through the transfer nip entrance point is 90 ° or less. 3. When the tangent line Ld drawn from the end of the upper guide to the lower guide to the lower guide intersects with the intersection point Pr, the radial line Rb of the photoconductor passing through the intersection Pr and the tangent line Ld. The image forming apparatus according to claim 1, wherein the angle α formed is 150 ° or less. 4. The length of the tangent line La (the distance from the transfer nip entrance point to the contact point Pa with the lower guide Pa) is calculated from the length of the tangent line Lb (the distance from the transport nip exit point to the contact point Pb with the lower guide). The image forming apparatus according to claim 1, wherein the image forming apparatus is also shortened. 5. The image forming apparatus according to claim 1, wherein a portion of the lower guide surface on which the paper slides is formed of a metal member having a smooth surface. 6. The image forming apparatus according to claim 5, wherein the metal member is grounded. 7. The image forming apparatus according to claim 5, wherein a groove is formed in a portion of the metal member on the transfer device side. 8. The image forming apparatus according to claim 1, wherein a portion of the lower guide surface with which the sheet comes into contact is formed by an outer peripheral surface of the idle roller. 9. The method according to claim 1, wherein an extension portion of a straight line connecting the end portion of the lower guide on the transfer portion side and the contact point Pa is located closer to the photoconductor than the center of rotation of the transfer roller. An image forming apparatus according to claim 2.