JP2000231282A - Intermediate transfer body unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an intermediate transfer body unit capable of reducing the space required to be attached and detached to/from an image forming device as much as possible, and capable of miniaturizing the image forming device itself in the intermediate transfer unit for mediating the transfer of the toner image from the image carrier to a recording sheet in the image forming device. SOLUTION: In the span of a transfer belt provided with a primary transfer position of the toner image, a moving roll 39 for making the transfer belt away from and nearer to the image carrier is allowed to abut on a tension roll 42 for applying tension to the transfer belt. Then the shifting roll 39 and the tension roll 42 are arranged so as to satisfy the following inequality, S1>S2, when comparing a space S1 eliminated by making the transfer belt away from the image carrier, and the space S2 newly generated by the tension roll 42 due to the said operation, in a space enclosed by the belt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intermediate transfer unit for transferring a toner image between a photosensitive drum and a recording sheet in an image forming apparatus such as an electrophotographic copying machine or a laser printer. More particularly, the present invention relates to an improvement in a structure required when an intermediate transfer unit having an endless transfer belt is attached to and detached from an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic copying machine or a laser printer, a toner image formed on a photosensitive drum according to image information is primarily transferred to an endless intermediate transfer belt. There is known an image transfer apparatus configured to secondarily transfer such a toner image from an intermediate transfer belt (hereinafter, referred to as a “transfer belt”) to a recording sheet. In particular,
In a color copying machine, a color printer, or the like that requires superposition of toner images of a plurality of colors, the toner images are repeatedly transferred from the photosensitive drum to the transfer belt, so that the positions of the plurality of toner images on the belt are changed. Many types using such a transfer belt have been proposed because they can be aligned.

Usually, the transfer belt is wound around a plurality of transport rolls, and the biased tension roll is brought into contact with the inside of the transfer belt so that the transfer belt always rotates at a predetermined tension without slack. It is configured.

Further, in this type of image forming apparatus, in order to improve the maintainability of the transfer belt and to make it easy to replace the transfer belt, the transfer belt has been unitized. It is configured as an intermediate transfer body unit together with the rotated transport rolls, tension rolls, and the like, and is configured to be freely detachable from the front of the image forming apparatus.

However, since the toner image is transferred from the photosensitive drum to the transfer belt, when the intermediate transfer unit is mounted on the image forming apparatus,
If the transfer belt is in contact with the photoconductor drum and the intermediate transfer body unit is pulled out of the image forming apparatus as it is, the photoconductor drum will be damaged by sliding friction with the transfer belt.

For this reason, in the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 9-325622, the intermediate transfer body unit is configured to be able to swing between the retracted position and the mounting position in the image forming apparatus. When such a unit is replaced, the entire unit that has been set at the mounting position is reset to the retracted position, and a gap is formed between the transfer belt and the photosensitive drum before the unit is pulled out. I was

In the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 7-199678, a swingable movable roll is disposed adjacent to a primary transfer position of a toner image on a transfer belt, and an intermediate transfer body unit is provided. When mounted on the image forming apparatus, the transfer roller pushes up the transfer belt from the inside,
This ensures contact between the transfer belt and the photosensitive drum, while releasing the intermediate transfer member unit from the image forming apparatus when the transfer belt is lifted by the moving roll, thereby releasing the transfer belt and the photosensitive drum. And a sufficient gap between them.

[0008]

However, in the former (JP-A-9-325622) image forming apparatus,
Since the entire intermediate transfer body unit swings between the mounting position and the retracted position in such an apparatus, a space around the mounted intermediate transfer body unit is large enough to allow the unit to swing. Need to be secured. By setting the intermediate transfer unit at the retracted position, the size of this space must be the same as the space created on the photosensitive drum side of the unit, and the space required for attaching and detaching the intermediate transfer unit is required. Therefore, there is a problem that the size of the image forming apparatus itself becomes large.

In the latter image forming apparatus (Japanese Patent Application Laid-Open No. Hei 7-199678), although the entire intermediate transfer unit is not swung, when the transfer belt is released from the state in which the transfer belt is lifted up by the movable roll, the image forming apparatus is released. Since the transfer belt is relaxed by the distance, the tension roll pushes the transfer belt outward, and the tension roll is in contact with the belt span opposite to the primary transfer position. A space of the same size as the gap created between the transfer belt and the photosensitive drum by the release must also be easily provided on the tension roll side, and also in the image forming apparatus for attaching and detaching the intermediate transfer unit. There was a problem that a useless space had to be secured.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to minimize the space that must be secured in an image forming apparatus for mounting and removing the apparatus. Accordingly, an object of the present invention is to provide an intermediate transfer unit that can contribute to downsizing of the image forming apparatus itself.

[0011]

In order to achieve the above object, an intermediate transfer body unit according to the present invention is configured by looping an endless transfer belt around a plurality of transport rolls.
An intermediate transfer body unit which is detachably provided to the image forming apparatus and is configured to secondarily transfer a toner image primarily transferred from the image carrier to the transfer belt to a recording sheet in the image forming apparatus. Assuming that the primary transfer position is provided on a belt span formed between a pair of transport rolls, and that the transfer belt is pushed up from the inside in the belt span including the primary transfer position, and the transfer belt and the When the unit is brought into contact with the image carrier, when the unit is removed from the image forming apparatus, the push-up state is released and the transfer belt that separates the transfer belt from the image carrier is provided. And a tension roll contacting the inside of the transfer belt, and the transfer belt is separated from the image carrier in the space surrounded by the transfer belt. And the space S ₁ that is extinguished by, when the tension roll is compared with the space S ₂ newly created by the separation operation, S _1> that the mobile roll and the tension roll is arranged such that the S ₂ It is characterized by the following.

According to such technical means, the moving roll is in contact with the transfer belt in the span of the transfer belt formed between the pair of transport rolls, that is, in the belt span. When the body unit is mounted on the image forming apparatus, the transfer belt pushes up the transfer belt from the inside, so that the image carrier on which the toner image is formed can be brought into contact with the transfer belt. On the other hand, when the intermediate transfer body unit is removed from the inside of the image forming apparatus, the transfer belt is released from the state in which the transfer belt is pushed up, so that the transfer belt is separated from the image carrier, and the image carrier is damaged. And the intermediate transfer unit of the present invention can be pulled out of the image forming apparatus.

In the case where the transfer belt is lifted by the moving roll and the intermediate transfer unit is detached, the transfer belt is lifted by the moving roll and the transfer belt is relaxed. Since the tension roll pushes the transfer belt outward, a space is required around the intermediate transfer body unit in the image forming apparatus to allow the tension roll to move outward.

Here, of the space surrounded by the transfer belt, a space S ₁ which disappears when the transfer belt is separated from the image carrier, and a space S ₁ newly created by the outward movement of the tension roll. Space S
_In the present invention, since the tension roll is provided in the same belt span as the moving roll in the present invention, the spaces S ₁ and S ₂ are located on the same side of the intermediate transfer body unit. become. Since the space S ₁ is contacting the transfer belt to the image carrier, that is, space is required to primarily transferred toner image on the transfer belt, around the intermediate transfer unit in an image forming apparatus in space since the space for S ₁ is provided inevitably space located on the side of the same space S ₁ S
₂ can be created using this space. That is, the image forming the space S ₁ and S ₂ are required and share a portion of the space that is needed around the intermediate transfer unit in an image forming apparatus, when that much of the unit removable only The space in the device can be reduced.

Moreover, when comparing the space S ₁ disappearing when the unit is attached and detached with the space S ₂ created, S ₁ > S
_{Since the} moving roll and the tension roll are arranged so as to be 2, it is necessary to provide almost unnecessary space around the intermediate transfer body unit in the image forming apparatus, which is required only when the unit is attached and detached. Absent.

In order to make the space S ₂ created by the movement of the tension roll smaller than the space S ₁ disappeared by the retreat of the moving roll (S ₂ <S ₁ ), the space S ₂ is located within the same span of the transfer belt. The arrangement of the moving roll and the tension roll may be devised.

For example, as shown in FIG.
With the belt 101 wrapped around the roll 100 between
Assuming that the roll 100 is raised by the distance h,
D is the belt length between A and B before the₁,Up
The belt length between A and B after ascending is d _TwoThen, the belt
Wrap angle θ of roll 101 with respect to roll 100 is large
In short, the belt 101 between A and B accompanying the rise of the roll 100
Perimeter change (d_Two-D₁) Becomes larger. Therefore,
This is caused by moving the transfer belt away from the image carrier.
The transfer belt is moved by moving the tension roll.
Transfer to the tension roll
The greater the belt wrap angle, the higher the tension
The amount of roll movement can be reduced. Also transfer
Belt relaxation is caused by retraction of the moving roll.
The transfer belt wraps against the tension roll.
If the angle is greater than the transfer roll,
The moving amount of the tension roll is smaller than the retracting amount of the moving roll.
Should be smaller.

That is, in the present invention, the wrap angle formed by the moving roll and the transfer belt is θ ₁ ,
When the wrap angle of the transfer belt and the tension roll to form a theta _2, if always set to θ ₁ <θ _2, the space S ₂ is created than the space S ₁ that disappears when attachment and detachment of the units Therefore, the space provided around the intermediate transfer body unit in the image forming apparatus can be made as small as possible.

Further, as shown in FIG. 10, a belt 102 having a constant length L is stretched between two points CD having a sufficient space via a point E slightly displaced from the line segment CD. Is assumed. Assuming that the height of the point E with respect to the line segment CD when the point E is located substantially at the center between the CDs is h, and that when the point E is close to the point C is H, the distance between the CDs is If h is sufficiently small, H <h. Therefore, when focusing on the distance between the transport roll forming the belt span and the moving roll or the tension roll, if the tension roll is closer to the transport roll than the moving roll, the transfer belt is moved from the image carrier. The moving amount of the tension roll when separated is smaller than the retracted amount of the moving roll.

That is, in the present invention, the distance between the moving roll and the nearest transport roll adjacent thereto is d.
_1, when the distance between the nearest transport rolls adjacent thereto and the tension roll was d _2, always d _1> If it is set to d _2, space disappears when attachment and detachment of the units S
₁ becomes smaller toward the space S ₂ is created from, is the space provided around the intermediate transfer unit in an image forming apparatus can be reduced as much as possible.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an intermediate transfer unit according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows an example of a digital color copier equipped with an intermediate transfer unit according to the present invention. This copier has a platen 10
An image input unit 1 for optically reading image information of a document 11 placed on the image input unit and converting the image information into electrical image data by a CCD sensor 12, based on image data transferred from the image input unit 1. And an image output section 2 for forming an image on a recording sheet P. Further, the image input section 1 is configured to automatically feed a document 11 to a platen 10.
The DF 13 can be attached.

The image output unit 2 forms a toner image on the photosensitive drum 20 based on the image data transferred from the image input unit 1, and then primary-transfers the toner image onto an endless transfer belt 3. Further, a recording image is formed on the recording sheet P by secondary-transferring the toner image on the transfer belt 3 onto the recording sheet P. The recording sheet P on which the toner image has been secondary-transferred passes through the fixing device 4. The paper is discharged onto the discharge tray 50.

The photosensitive drum 20 is rotated in a direction indicated by an arrow at a predetermined process speed, and around the photosensitive drum 20, the surface of the photosensitive drum 20 is uniformly charged to a predetermined background portion potential. A charging corotron 21, a laser beam scanner 22 that exposes the photosensitive drum 20 with a laser beam modulated based on image data and forms an electrostatic latent image on the photosensitive drum 20, and black, yellow, magenta, and cyan And a rotary developing unit 23 for developing an electrostatic latent image on the photosensitive drum by any one of the developing units, and a developing unit 23 on the photosensitive drum 20 prior to the primary transfer of the toner image to the transfer belt 3. A pre-transfer treatment corotron 24 for removing potential and a cleaner 25 for removing residual toner on the photosensitive drum 20 after the primary transfer of the toner image is disposed. That.

On the other hand, the transfer belt 3 is wound around a plurality of rolls and rotates in the direction of the arrow, and
The toner images of each color sequentially formed on the transfer belt 3
After the multiple transfer to the recording sheet P, the secondary transfer is collectively performed from the transfer belt 3 to the recording sheet P. At a position facing the photosensitive drum 20 with the transfer belt 3 interposed therebetween, a primary transfer roll 30 for forming a transfer electric field between the photosensitive drum 20 and the primary transfer roll 30 is provided. Is the secondary transfer roll 31 and the counter electrode roll 3
The recording sheet P is inserted between the secondary transfer roll 31 and the transfer belt 3 to receive the transfer of the toner image. A belt cleaner 33 that removes paper dust and residual toner from the surface of the transfer belt 3 after the secondary transfer is provided between the secondary transfer position and the primary transfer position in the rotation path of the transfer belt 3. Is provided.

Below the image output unit 2, four-stage sheet feeding cassettes 5a to 5d containing recording sheets P of different sizes are provided, and the recording sheets P of the size selected in the copying operation are provided. Is rotated from one of the sheet feeding cassettes by the rotation of the feed roller 51.
To be sent out. A plurality of sheet transport rolls 52 are provided on the transport path of the recording sheet P from each of the sheet feeding cassettes 5a to 5d to the secondary transfer position of the toner image, and registration is performed immediately before the secondary transfer position. The registration roll 53 is provided with the sheet feeding cassettes 5a to 5d.
Is fed to the secondary transfer position at a predetermined timing synchronized with the timing of writing the electrostatic latent image on the photosensitive drum 20.

In FIG. 1, reference numeral 26 denotes an image processing which processes the image data transferred from the image input unit 1 to the image output unit 2 in accordance with the content of the copying operation and then supplies the processed image data to the laser beam scanner 22. , Reference numeral 54 denotes a manual feed tray used for manual feeding of the recording sheet P, reference numeral 55 denotes a sheet conveying belt for feeding the recording sheet P on which the toner image has been secondarily transferred to the fixing device 4, and reference numeral 56 denotes a recording sheet. P
This is an inverter path for inverting the recording sheet P and feeding it from the fixing device 4 to the secondary transfer position at the time of double-sided copying.

In the color copying machine of the present embodiment configured as described above, the laser beam scanner 22 exposes the photosensitive drum 20 based on the image information of the original taken in by the image input unit 1, and first, the photosensitive drum 20 is exposed. An electrostatic latent image corresponding to black is written on the body drum 20. on the other hand,
In the rotary developing unit 23, a developing device for black toner is set at a position facing the photosensitive drum 20, and the electrostatic latent image is developed by the black developing device with a slight delay from its writing timing. Then, the black toner image thus formed is transferred to the primary transfer roll 3.
0, the image is primarily transferred onto the transfer belt 3, and the transfer belt 3 rotates while carrying the toner image. When the developing process by the black developing device is completed, the transfer belt 3
The developing device is replaced before the rotation cycle is completed, and the developing device for yellow toner is set at a position facing the photosensitive drum 20 by rotating the rotary developing unit 23 by 90 °.

Thereafter, these operations are repeated for each rotation cycle of the transfer belt 8, and each time, the yellow, magenta and cyan toner images are transferred from the photosensitive drum 20 to the transfer belt 3. , A superimposed toner image of four color toner images is formed. The full-color multi-transferred toner image thus formed is secondarily transferred to the recording sheet P sent from the registration roll 53 at a predetermined timing, and the unfixed toner image is transferred to the recording sheet P. The sheet is discharged to the discharge tray 50 via the fixing device 4.

In order to improve the maintainability of the transfer belt 3, the transfer belt 3 is configured as an intermediate transfer unit U together with a plurality of rolls around which the transfer belt 3 is wound, and is mounted on the image output unit 2 of the color copying machine. And
It can be inserted and removed from the front side of the image output unit 2 as needed. FIG. 2 shows the intermediate transfer body unit U. A plurality of rolls around which the transfer belt 3 is wound are supported at both axial ends by a front side frame 34 and a rear side frame 35. It is configured to be able to rotate freely between them.

FIG. 3 shows the arrangement of the respective rollers when the intermediate transfer unit U is mounted on the image output unit. In the figure, reference numeral 36 denotes a drive roll for transmitting rotation of a motor (not shown) to the transfer belt 3, reference numeral 37 denotes a steering roll for restricting movement of the transfer belt 3 in the width direction during rotation, and reference numeral 32. The reference numeral 38 denotes a counter electrode roll disposed at a secondary transfer position of a toner image, and the reference numeral 38 denotes a driven roll for guiding the transfer belt 3 between the steering roll 37 and the counter electrode roll 32. U, which is fixed and determines the rotation path of the transfer belt 3. Therefore, these rolls correspond to the transport roll in the present invention.

A primary transfer position for transferring a toner image from the photosensitive drum 20 to the transfer belt 3 is provided between the drive roll 36 and the steering roll 37, and the primary transfer is biased by a spring 30a. At a position where the roll 30 faces the photosensitive drum 20, the transfer belt 3
In contact with the back side of In order to ensure that the transfer belt 3 is in contact with the photosensitive drum 20, a drive roll 36
A moving roll 39 for pushing up the transfer belt 3 from the inside is provided in a span (hereinafter, referred to as a “belt span”) of the transfer belt 3 formed by the transfer belt 3 and the steering roll 37. A cam 41 that rotates about a support shaft 40 is provided below the moving roll 39, and the moving roll 39 is configured to move up and down according to the set position of the cam 41. The support shaft 40 of the cam 41 is connected to an attachment / detachment operation handle (not shown) of the intermediate transfer body unit U. When the handle is rotated to the attachment position in a state where the unit U is attached to the image output unit, the cam 41 is rotated. The roll 39 pushes up the transfer belt 3 by the rotation of
The transfer belt 3 comes into contact with the photosensitive drum 20. As a result, the toner image can be transferred from the photosensitive drum 20 to the transfer belt 3.

In order to prevent the transfer belt 3 from being loosened between the rolls and always apply a predetermined tension to the transfer belt 3, a tension roll is provided in a belt span formed by the drive roll 36 and the steering roll 37. 42 are provided. The tension roll 42 has a substantially L-shaped swing arm 4 swinging about a support shaft 43.
The other end of the swing arm 44 is pulled by a spring 45 so that the swing arm 44 is always in contact with the inside of the transfer belt 3 in a biased state.

On the other hand, FIG. 5 shows a state in which the attaching / detaching operation handle of the intermediate transfer unit U is set to the detached position, and the movable roll 39 is retracted from the position where the transfer belt 3 is pushed up. By the retreat of the moving roll 39, the raised state of the transfer belt 3 is released, and the transfer belt 3 is separated from the photosensitive drum 20. As a result, it is possible to remove the intermediate transfer unit U from the image output unit 2 of the copying machine while preventing the transfer belt 3 and the photosensitive drum 20 from slidingly contacting each other.

At this time, it is inconvenient if the primary transfer roll 30 urged by the spring 30a pushes the transfer belt 3 toward the photosensitive drum 20.
The primary transfer roll 30 is configured to come into contact with and separate from the transfer belt 3 in accordance with the vertical movement of the moving roll 39.
As shown in FIG. 5, the moving roll 39 is provided at the tip of a support arm 47 that swings around a support shaft 46, and the support arm 47 is configured such that the moving roll 39 always moves according to the set position of the cam 41. Spring 4 to move up and down
8 urged in the direction of the cam 41. The support arm 47 is disposed so as to hold down the rotation axis of the primary transfer roll 37. When the movable roll 39 is lowered by the rotation of the cam 41, the primary transfer roll 39 is moved from the transfer belt 3 by the swinging support arm 47. The primary transfer roll 37 is pushed down in the direction in which the primary transfer roller 37 moves away from the transfer belt 3 in conjunction with the moving roll 39.

Here, when the cam 41 is rotated to release the state where the transfer belt 3 is pushed up by the moving roll 39,
Drive roll 36 and steering roll 3
Although the transfer belt 3 is loosened between the transfer belt 7 and the transfer belt 7, the tension roller 42 urged from the inside to the outside of the transfer belt 3 abuts in the belt span. When the transfer belt 3 is retracted, the tension roll 42 pushes up the transfer belt 3 outward, so that the transfer belt 3 is prevented from loosening.

FIG. 6 shows a comparison between the space enclosed by the transfer belt 3 when the intermediate transfer unit U is attached to the image output unit 2 and when the intermediate transfer unit U is removed. The space S ₁ indicated by hatching in the figure is released by releasing the transfer belt 3 from being pushed up by the moving roll 39, that is, by separating the transfer belt 3 from the photosensitive drum 20 for extracting the unit U. , A space outside the transfer belt 3. The space indicated by hatching S ₂ is a space newly inside the transfer belt 3 due to the movement of the tension roll 42 at that time.

As is apparent from this figure, in the intermediate transfer body unit U of this embodiment, the moving roll 39 and the tension roll 42 are arranged in the same belt span formed by the drive roll 36 and the steering roll 37. Therefore, when the unit U is extracted from the image output unit 2, the space S ₁ outside the transfer belt 3 and the space S ₂ inside the transfer belt 3 are on the same belt span, that is, the space S _{1 of} the intermediate transfer unit U. It will occur adjacent to each other on the same side. The space S ₁ is a space necessary for the primary transfer of the toner image to the transfer belt 3. The space for the space S ₁ is provided on the photosensitive drum side of the intermediate transfer unit U mounted on the image output unit 2. since There are provided necessarily, it is the space S ₂ by extruding the tension roller 42 the transfer belt 3 in the mounting and dismounting of the intermediate transfer unit U to the outside is generated in this embodiment, such space S
Otherwise there is no need to provide space in the image output unit 2 for _2.

Further, in this embodiment, when the transfer roller 39 pushes the transfer belt 3 toward the photosensitive drum 20, the wrap angle of the transfer belt 3 with respect to the transfer roller 39 is θ ₁ , as shown in FIG. As shown in FIG. 8, assuming that the wrap angle of the transfer belt 3 with respect to the tension roll 42 is θ ₂ , the moving roll 39 and the tension roll 42 are arranged so that θ ₁ <θ _2. Thus, the space S ₂ newly required is always smaller than the space S _{1 that} has disappeared due to the retreat of the moving roll 39. That is, when the slack of the transfer belt 3 caused by the retreat of the moving roll 39 is eliminated by the movement of the tension roll 42, as described with reference to FIG.
Is greater than the wrap angle, the amount of movement of the tension roller 42 is smaller than the height h ₁ of the space S ₁ shown in FIG. 6, it is the space S ₂ is smaller than the space S _1.

Further, in this embodiment, the moving roll 39 is disposed substantially at the center of the belt span formed by the drive roll 36 and the steering roll 37, while the tension roll 42 is disposed close to the steering roll 37. The distance between the moving roll 39 and the drive roll 36 is L
_1, when the distance between the tension roller 42 and the steering roller 37 was set to L _2, is set to L _1> L _2. Therefore, when the slack of the transfer belt 3 caused by the retreat of the moving roll 39 is eliminated by the movement of the tension roll 42, as described with reference to FIG.
Tension roll 4 located near the end of the belt span
2 the amount of movement is smaller than the height h ₁ of the space S ₁ in the substantially center of the belt span, the space S ₂ In this respect is to become smaller than the space S _1.

As a result, in the intermediate transfer body unit U of this embodiment, even when the transfer belt 3 is separated from the photosensitive drum 20 when the intermediate transfer body unit U is extracted from the image output section 2 of the copying machine, the transfer belt 3 However, the amount of swelling outward by the tension roll 42 can be reduced as much as possible.
Therefore, there is no need to form a useless space around the unit U in order to avoid interference between the device around the unit U mounted on the image output unit 2 and the transfer belt 3.
The size of the image output unit and, consequently, the size of the entire copying machine can be reduced accordingly.

[0041]

As described above, according to the intermediate transfer unit of the present invention, of the space surrounded by the transfer belt, the space S ₁ that disappears when the transfer belt is separated from the image carrier. And the newly created space S
₂ is located on the same side of the intermediate transfer unit, and the created space S ₂ is smaller than the disappearing space S ₁ (S ₂ <S ₁ ). There is almost no need to provide unnecessary space around the body unit only when the unit is attached or detached,
Accordingly, the size of the image forming apparatus to which the unit is mounted can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the structure of a color copying machine on which an intermediate transfer body unit of the present invention is mounted. It is a front view showing an example of a robot hand.

FIG. 2 is a perspective view showing an appearance of a friend transfer unit according to the embodiment.

FIG. 3 is a schematic diagram showing an arrangement of various rolls and a rotation path of a transfer belt in a state where the intermediate transfer body unit according to the embodiment is mounted in a copying machine.

FIG. 4 is a schematic diagram showing an arrangement of various rolls and a state of a transfer belt when the intermediate transfer body unit according to the embodiment is detached from a copying machine.

FIG. 5 is a schematic diagram illustrating a moving mechanism of a moving roll and a primary transfer roll according to an embodiment.

FIG. 6 is a diagram comparing the state of tension of the transfer belt before and after the transfer belt is separated from the photosensitive drum.

FIG. 7 is a diagram illustrating a wrap angle of a transfer belt with respect to a moving roll according to the embodiment.

FIG. 8 is a diagram illustrating a wrap angle of a transfer belt with respect to a tension roll according to the embodiment.

FIG. 9 is a diagram illustrating the relationship between the length of a belt wound around a roll between two points AB and the wrap angle of the belt with respect to the roll.

FIG. 10 is a diagram illustrating the relationship between the height h or H of the belt wound around point E between two points CD and the position of point E between the CDs.

[Explanation of symbols]

2 ... Image output unit (image forming apparatus), 3 ... Transfer belt, 3
Reference numeral 6: drive roll (conveying roll), 37: steering roll (conveying roll), 39: moving roll, 42: tension roll, U: intermediate transfer body unit

Claims (3)

[Claims] 1. An image forming apparatus comprising: an endless transfer belt wound around a plurality of transport rolls; and a detachable transfer belt provided in an image forming apparatus. In the intermediate transfer unit configured to secondary-transfer the primary-transferred toner image to a recording sheet, the primary transfer position is provided on a belt span formed between a pair of transport rolls. In the belt span including the position, the transfer belt is pushed up from the inside to bring the transfer belt into contact with the image carrier, and when the unit is extracted from the image forming apparatus, the pushed up state is released and the transfer is performed. A moving roll for separating the belt from the image carrier, and a tension roll for constantly abutting against the inside of the transfer belt in a urged state; Of the space surrounded by shooting belt, and the space S ₁ that disappeared by which is spaced such a transfer belt from the image bearing member, when the tension roller by the separation operation is compared with the space S ₂ newly created , S ₁ >
Intermediate transfer unit, characterized in that the mobile roll and the tension roll is arranged such that S _2. 2. The intermediate transfer body unit according to claim 1, wherein a wrap angle formed by the moving roll and the transfer belt is θ ₁ , and a wrap angle formed by the tension roll and the transfer belt is θ _2. , Always θ ₁
< ₂ . An intermediate transfer body unit, wherein θ ₂ is set. 3. The intermediate transfer unit according to claim 1,
And the nearest transport roll adjacent to the transport roll.
Distance d₁, Next to the above tension roll
The distance to the nearest transport roll that is in contact_TwoAnd when
Always d₁> D _TwoIntermediate characterized by being set to
Transfer unit.