JP2001125390A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device equipped with an intermediate transfer belt capable of restraining the dimension in the height direction of the entire intermediate transfer belt stretched and laid over rolls to be as small as possible without spoiling original performance required for the intermediate transfer belt and also contributing to the reduction of the height of the entire device. SOLUTION: The intermediate transfer belt 21 stretched and laid over two principal rolls 22 and 23 to be flat is installed so that its longitudinal direction may be nearly horizontal in a device main body 1. Either roll 22 or 23 is used as a backup roll for secondary transfer so as to constitute one part of the secondary transfer part, and the other roll 23 is used as a driving roll and also as a steering roll for correcting the traveling deviation of the belt 21 by displacing the entire roll.

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 using an intermediate transfer belt, such as a copying machine, a printer, and a multifunction machine, and more particularly, to an image formed by improving a mechanism relating to the intermediate transfer belt. The present invention relates to a forming apparatus.

[0002]

2. Description of the Related Art In recent years, an intermediate transfer system may be employed in a color image forming apparatus such as an electrophotographic color copying machine or a color printer. A color image forming apparatus employing this intermediate transfer system is, for example, shown in FIG.
As shown in FIG. 2, toner images formed on an image carrier 100 such as a photosensitive drum are sequentially or collectively transferred to a drum-shaped intermediate transfer member 200 (a in the drawing) or a belt-shaped intermediate transfer member 300 (b in the drawing). And the primary transfer, and the intermediate transfer members 200 and 300
The toner image after the primary transfer is secondarily transferred to a transfer material 400 such as a recording sheet, thereby forming a color image or the like. In this case, one image carrier 10
An image forming apparatus of a type in which toner images of each color component are sequentially formed on one image carrier by using 0, and a toner image of each color component is distributed by each image carrier by using a plurality of image carriers 100. There is an image forming apparatus of a type formed by forming an image.

[0003]

However, a color image forming apparatus using such a drum-shaped or belt-shaped intermediate transfer body 200, 300 does not use the intermediate transfer body. In comparison, the arrangement of the mechanisms related to the intermediate transfer members 200 and 300 in the apparatus main body increases the height (dimensions) of the apparatus, and it is difficult to reduce the size of the apparatus.

[0004] Among them, an image forming apparatus using a drum-shaped intermediate transfer member 200 has a plurality of image carriers, especially in the case of a type in which a plurality of image carriers 100 are arranged around the intermediate transfer member 200. Since it is necessary to set the diameter of the drum to some extent in order to secure a drum peripheral surface area that can be provided, the height H ₂₀₀ of the entire intermediate transfer drum 200 tends to be large, which results in an increase in the apparatus height. It is difficult to lower.

In many image forming apparatuses using a belt-shaped intermediate transfer member 300, the intermediate transfer belt 300 is stretched around at least three rolls 310, 320, and 330, for example, at each vertex of the inverted triangle. The roll 3 arranged at the lower side of the three rolls arranged correspondingly
30 is used as a backup roll at the time of the secondary transfer, and constitutes a part of the secondary transfer portion. Therefore, the dimension H ₃₀₀ in the height direction of the entire intermediate transfer belt 300 stretched on the roll is large. It is also difficult to reduce the height of the apparatus.

The applicant of the present invention has previously proposed a method of increasing the gripping force of the drive roll to prevent the intermediate transfer belt from slipping.
As shown in FIG. 11, two rotating rolls 350, 360
An image forming apparatus in which a driving roll 370 is disposed so as to be pressed from the outer peripheral surface of the intermediate transfer belt 300 between the intermediate transfer belt 300 (Japanese Patent Laid-Open No. Hei 10-260590). However, in this case, since at least three rolls 350, 370, and 360 need to be arranged at intervals in the vertical direction, the height dimension of the entire intermediate transfer belt 300 stretched over the rolls is required. H ₃₀₀ is inevitably large, it is difficult to reduce the device height. Also,
Since the drive roll 370 comes into contact with the outer peripheral surface serving as the transfer surface of the intermediate transfer belt 300, there are disadvantages such as that the roll surface is stained by toner or the like, and the outer peripheral surface of the belt is damaged.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to minimize the height dimension of the entire intermediate transfer belt stretched over a roll without impairing the original performance required of the intermediate transfer belt. It is an object of the present invention to provide an image forming apparatus provided with an intermediate transfer belt that can be suppressed and contribute to reduction of the height of the entire apparatus.

[0008]

The (first) image forming apparatus of the present invention which achieves the above object is an endless intermediate transfer which is stretched over at least two main rolls and rotated in a fixed direction. A belt, wherein the toner image formed on the image carrier is primarily transferred onto the intermediate transfer belt, and then the toner image is secondarily transferred onto a material to be transferred, thereby forming an image. Is installed so that its longitudinal direction is substantially horizontal in the apparatus body, and
One of the two main rolls is used as a backup roll for secondary transfer to constitute a part of a secondary transfer portion. In this case, when using a belt of a type in which a rib is formed on at least one side end as an intermediate transfer belt and the rib is rotated while being regulated by an end surface of a main roll, the intermediate transfer belt on which the rib is formed is used. It is preferable to reduce the number of rolls on which the sheet is stretched as much as possible.

In the first image forming apparatus, since the intermediate transfer belt is stretched around at least two main rolls, the intermediate transfer belt has a flat shape as a whole, and therefore has a small dimension in the height direction. Become. Since such a flat intermediate transfer belt having a small dimension in the height direction is arranged in a state where the longitudinal direction thereof is substantially horizontal in the apparatus main body, the height of the apparatus is increased by disposing the intermediate transfer belt. Minutes are reduced as much as possible. Also, since the wrap angle of the intermediate transfer belt with the backup roll increases, during the secondary transfer,
The transfer material supplied in a state of being pressed against the outer peripheral surface of the intermediate transfer belt stretched on the roll is easily peeled off from the outer peripheral surface of the belt.

In the first image forming apparatus, the other main roll other than the secondary transfer backup roll is used as a drive roll for transmitting rotational power to the intermediate transfer belt, and at the same time, the entire roll is displaced. In this case, it may be configured to be used as a steering roll for correcting a traveling deviation in a direction orthogonal to the rotation direction of the intermediate transfer belt.

In the second image forming apparatus constructed as described above, the rotation drive of the intermediate transfer belt and the correction of the traveling deviation in the direction orthogonal to the rotation direction are performed by only one main roll. In addition, since the wrap angle of the intermediate transfer belt with the drive roll increases, the grip force increases, and the rotational power of the drive roll is accurately transmitted to the intermediate transfer belt. As a result, the intermediate transfer belt rotates accurately and stably. I will be. Further, the wrap angle of the intermediate transfer belt with the steering roll is also increased, so that the intermediate transfer belt can be quickly displaced with respect to the steering operation, and the correction sensitivity is improved.

Further, in the second image forming apparatus, a belt surface between the driving roll and the backup roll for secondary transfer, which supports the intermediate transfer belt from the inner peripheral surface thereof and contacts the image carrier. It is preferable to arrange at least two auxiliary rolls for determining the following. The at least two auxiliary rolls are preferably rolls having a roll diameter smaller than the two main rolls (drive roll and backup roll for secondary transfer). Further, it is preferable that the auxiliary roll is disposed at a position that supports an intermediate transfer belt region that is downstream of the driving roll in the belt rotation direction and upstream of the backup roll in the belt rotation direction.

In the third image forming apparatus configured as described above, the belt surface on which the image carrier comes into contact is determined between at least two auxiliary rolls. Thus, since the belt surface is located between at least two auxiliary rolls, there is no displacement (fluctuation) due to the steering operation of the steering roll (drive roll). In particular, when a plurality of image carriers are provided, the contact state of each image carrier with the intermediate transfer belt is the same.

In the third image forming apparatus, one of the at least two auxiliary rolls, which is provided at both ends, applies tension to the intermediate transfer belt and applies the image to the intermediate transfer belt. It is preferable to use the tension roller as a tension roll that adjusts the deflection of the intermediate transfer belt by displacing the reference surface in the same positional relationship as the belt surface with which the carrier contacts.

In the fourth image forming apparatus having the above-described configuration, the deflection of the intermediate transfer belt is adjusted by displacing the tension roll in the reference plane having the same positional relationship as the belt surface on which the image carrier is in contact. Is done. During the deflection adjustment, the tension roll is displaced within the reference plane, and therefore, the belt surface in contact with the image carrier is not displaced along with the displacement of the roll (the tension roll is not displaced from the other auxiliary roll). (With support in between).

On the other hand, in the third image forming apparatus, three or more auxiliary rolls are provided, and one of the auxiliary rolls provided at both ends is used to apply tension to the intermediate transfer belt and to apply the tension to the intermediate transfer belt. May be configured to be used as a tension roll for adjusting the deflection of the intermediate transfer belt by displacing the intermediate transfer belt in a direction to increase or decrease the pressing force on the intermediate transfer belt surface. In this case, the image carrier is not brought into contact with the belt surface between the tension roll and the auxiliary roll adjacent to the tension roll.

In the fifth image forming apparatus constructed as described above, the deflection of the intermediate transfer belt is adjusted by displacing the tension roll in the direction of increasing or decreasing the pressing force on the intermediate transfer belt surface. Further, the belt surface with which the image carrier comes into contact between two or more auxiliary rolls other than the tension roll at the one end side is determined. As a result, the belt surface is always located between at least two auxiliary rolls having no tension roll, and the tension roll comes into contact with the image carrier as in the case of the fourth image forming apparatus. Even if the tension roll is not configured to be displaced in the reference plane having the same positional relationship as the belt surface, the tension roll is not displaced (fluctuated) by being affected by the operation of adjusting the deflection of the tension roll.

Further, in the fourth or fifth image forming apparatus, it is preferable that the auxiliary roll disposed on the end side which is the secondary transfer backup roll side is used as a tension roll.

In the sixth image forming apparatus constructed as described above, since the tension roll is located on the downstream side in the rotation direction from the belt surface serving as the primary transfer portion in contact with the image carrier,
The rotation (moving) speed of the belt surface serving as the primary transfer portion is kept constant without being affected by the operation of the deflection adjustment of the tension roll and fluctuated.

In the sixth image forming apparatus, the intermediate transfer belt is supported between the secondary transfer backup roll and the tension roll from the inner peripheral surface side thereof, and the belt advance angle to the secondary transfer portion is provided. It is preferable to provide a pre-roll for determining the value.

In the seventh image forming apparatus constructed as described above, even if the belt advance angle of the intermediate transfer belt into the secondary transfer portion is adjusted due to the presence of the pre-roll, for example, the deflection roll of the tension roll is adjusted. Since it is always kept constant, the condition of the secondary transfer portion is constant, and good secondary transfer is possible.

The image carrier is a drum-shaped or belt-shaped photoconductor or dielectric. In addition, the number may be singular or plural, but the present invention is particularly effective for plural cases.

[0023]

[First Embodiment] FIGS. 1 and 2
1 shows a first embodiment of the present invention. FIG. 1 is a schematic explanatory view showing the overall configuration of an image forming apparatus according to the first embodiment, and FIG. 2 is an intermediate transfer belt employed in the image forming apparatus. It is explanatory drawing which shows a mechanism.

The image forming apparatus according to the first embodiment includes yellow (Y), magenta (M), cyan (C), and black (K) separately formed by four image forming units 10Y, 10M, 10C, and 10K. After the four color toner images are primarily transferred so as to be superimposed on the surface of the intermediate transfer belt 31 of the intermediate transfer mechanism 30, the toner images are secondarily transferred from the intermediate transfer belt 31 to the recording sheet P side as a material to be transferred. Is a color image forming apparatus capable of forming a so-called full-color image. This apparatus can also form a black and white image by operating only the black image forming unit 10K among the four image forming units.

First, all of the image forming units 10
Each of the above-described four color toner images is formed by an electrophotographic process, and is disposed at a substantially central portion of the image forming apparatus main body 1 with a horizontal space therebetween. Also, each of the image forming units 10 is basically
A photosensitive drum 11 as an image carrier that is rotated and driven at a predetermined speed, a charging roll device 12 that uniformly charges the surface of the photosensitive drum 11, and a surface corresponding to image information on the charged surface of the photosensitive drum 11 A latent image forming device 13 for exposing a light image to form an electrostatic latent image, a developing device 14 for developing the electrostatic latent image with toner of a predetermined color, and an intermediate transfer belt for transferring the toner image formed by the development In the same manner, a transfer roll device 15 for transferring the image to the transfer roller 21 and a drum cleaner 16 for cleaning the surface of the photosensitive drum 11 are provided.

Among them, the latent image forming device 13 emits laser beams LB-Y, LB-M and LB emitted from four semiconductor lasers (not shown) in accordance with image signals separated for each color.
-C, LB-K through a predetermined optical system to rotate the polygon mirror 17
After irradiating the photosensitive drum 11 with deflected scanning, scanning exposure is performed from diagonally below on each of the opposing photosensitive drums 11 via a plurality of reflecting mirrors (not shown). Reference numeral 18 in the figure
Is a transparent window for transmitting and emitting each of the laser beams LB from the housing box 13a of the latent image forming apparatus. Further, each developing device 14 includes a toner cartridge 19 containing a corresponding color toner (developer).
From the toner supply device (not shown). Further, a primary transfer bias having a polarity opposite to the charging polarity of the toner image on the photosensitive drum 11 is applied to the transfer roll device 15 from a bias power supply (not shown).

In each of the image forming units 10, the surface of the photosensitive drum 11 rotating in the direction of arrow A is uniformly charged by the charging roll device 12, and then the latent image forming device 13 is applied to the charged surface. An electrostatic latent image is written by scanning and exposing a laser beam LB corresponding to an image signal that has been color-separated from the image data. Thereafter, the latent image is developed with toner of each color supplied from the developing device 14. Finally, the toner image is transferred to the photosensitive drum 1
The primary transfer is performed on the surface of the intermediate transfer belt 21 passing between the transfer roller 1 and the transfer roll device 15 sequentially and electrostatically. The surface of the photosensitive drum 11 after the transfer is cleaned by a blade of a drum cleaner 16 or the like.

Next, as shown in FIGS. 1 and 2, the intermediate transfer mechanism 20 transfers an endless intermediate transfer belt 21 to a secondary transfer backup roll 22 and a drive roll 23 as main rolls. The whole is stretched so as to be elongated and flat, and between the backup roll 22 and the driving roll 23 and each roll 2
As three auxiliary rolls, which are supported near the inner peripheral surface of the intermediate transfer belt 21 at positions near the intermediate transfer belts 2 and 23 so as to determine the belt surfaces on which the photosensitive drums 11 of the respective image forming units 10 abut. The first idler roll 24, the second idler roll 25, and the tension roll 26 are stretched, and are driven to rotate in the direction of arrow B by the rotational power of the drive roll 23.

As shown in FIG. 1, the intermediate transfer mechanism 20 includes an intermediate transfer belt 21 stretched over the rolls 22 to 26 so as to be flat as described above.
The longitudinal direction is substantially horizontal in the apparatus main body 1, and the belt surface between the first idler 24 and the second idler roll 25 can be brought into contact with the photosensitive drum 11 of each image forming unit 10. It is arranged as follows. Further, at the position on the inner peripheral surface of the intermediate transfer belt 21 opposite to the position where the intermediate transfer belt 21 comes into contact with each photosensitive drum 11, the above-described transfer roll device 15 is disposed so as to press the belt 21 against each photosensitive drum 11. Thus, each primary transfer unit is constituted. Furthermore, at the position facing the backup roll 22,
A secondary transfer roll 30 for pressing the intermediate transfer belt 21 against the roll 22 is provided, and a bias power source (not shown) having the same polarity as the charged polarity of the toner image on the belt 21 is provided on the peripheral surface of the backup roll 22. The power supply roll 31 to which the secondary transfer bias is supplied is disposed so as to directly contact with the power supply roll 31, thereby forming a secondary transfer unit.

Further, in the intermediate transfer mechanism 20,
As shown in FIG. 1 or FIG. 2, a pre-roll 27 that supports the intermediate transfer belt 21 from the inner peripheral surface thereof between the tension roll 26 and the backup roll 22 and determines the angle of entry of the belt into the secondary transfer portion. Is connected. In FIG. 2, reference numeral 32 denotes a sheet conveyance guide for guiding the direction of entry of the recording sheet P into the secondary transfer portion, 35 denotes a belt cleaner for cleaning the surface of the intermediate transfer belt 21 (35a is a cleaning blade), and 36 denotes A roll cleaner (36a is a cleaning blade) for cleaning the surface of the secondary transfer roll 30, 37 is a belt home position detecting device for detecting a belt home mark formed on a side end of the intermediate transfer belt 21, and 38 is an intermediate transfer. This is a belt walk detection device that detects a deviation (offset or meandering) of a belt edge (one side end) position of the belt 21 in a direction perpendicular to the belt rotation direction B.

The toner image transferred (multiplied) to the intermediate transfer belt 21 of the intermediate transfer mechanism 20 is transferred to a secondary transfer roll 30 disposed opposite to the backup roll 22 with the rotation of the belt 21. The sheet is transported to the opposed secondary transfer section. Then, the toner image on the intermediate transfer belt 21 is sent out from the storage tray 40 in accordance with the image formation of the toner image and the secondary transfer timing, and is subjected to the secondary transfer through a sheet conveying path on which a roll 41, a registration roll 42 and the like are arranged. (Between the intermediate transfer belt 21 and the secondary transfer roll 30) of the recording sheet P having a predetermined size.
Secondary transfer is performed electrostatically. 1 indicates a conveyance path of the recording sheet P.

Subsequently, the recording sheet P on which the toner image has been transferred from the intermediate transfer belt 21 is naturally separated from the intermediate transfer belt 21 in the secondary transfer section, and then heated by a heating roll 46 in a roll nip type fixing device 45. And the toner image is subjected to heat fixing processing by passing through the nip portion of the pressure roll 47, and thereafter, the discharge roller 48
Is discharged to the outside of the apparatus main body 1 (sheet discharge storage section). Through the above process, a color image is formed on the recording sheet P.

In this image forming apparatus, the intermediate transfer belt 21 is stretched mainly on the backup roll 22 and the drive roll 23, and is supported by the three auxiliary rolls 24 to 26 so as to slightly expand downward. The entire belt is elongated and flat as described above, and the dimension E in the height direction is extremely small. Moreover, since the intermediate transfer belt 21 stretched in a flat shape is disposed such that the longitudinal direction thereof is substantially horizontal in the image forming apparatus main body 1, the intermediate transfer belt 21 is The increase in the height of the apparatus main body 1 due to the arrangement is extremely small. Thus, even in an image forming apparatus employing the intermediate transfer mechanism 20, the height of the apparatus can be reduced as much as possible.

In such an intermediate transfer belt 21, since the wrap angle β of the belt 21 with the backup roll 22 is increased as shown in FIG. 2 and the like, the recording sheet P after the secondary transfer is It is naturally peeled off from the intermediate transfer belt 21 portion (the portion stretched around the backup roll 22) in the next transfer portion. Therefore, in the secondary transfer portion of the intermediate transfer mechanism 20, there is no need to provide a separation auxiliary component such as a separation claw for assisting the separation of the recording sheet P from the intermediate transfer belt 21, and as a result, the separation auxiliary component It is not necessary to secure an installation space for this, so that an increase in the height H of the intermediate transfer belt 21 can be suppressed accordingly. In addition, the cost can be reduced because the separation assisting parts are not provided.

In the intermediate transfer mechanism 20,
As shown in FIG. 3, a steering mechanism 50 that adjusts the running state of the intermediate transfer belt 21 by displacing one end of the drive roll 23 in a certain adjustment direction J or K (steering operation) is provided. Therefore, the drive roll 23 is also used as a steering roll.

That is, the drive roll 23, which is also used as a steering roll, has a roll shaft 23b projecting from both ends of the roll body 23a.
It is rotatably supported via 52b. The drive roll unit housing 51 is supported by a bracket 50a that can swing on the fixed frame 1a of the apparatus main body 1 at a lower position on one end side in the roll axis direction, and at a position on the other end side. It is supported by a steering mechanism 50 described later. And the drive roll 23
Is configured such that the rotational power of the drive motor 53 is transmitted and rotated by a gear train in which a drive gear 54 attached to the output shaft of the drive motor 53 and a passive gear 55 attached to the roll shaft 23b mesh. . The rotation speed of the drive roll 23 is detected by a rotation speed detection mechanism such as a rotary encoder (not shown) attached to the roll shaft 23b, and the rotation state of the drive motor 53 is feedback-controlled based on the detected information. By doing so, it rotates stably at a predetermined speed.

The steering mechanism 50 includes a steering motor 56 such as a stepping motor, and an eccentric cam 57 attached to an output shaft 56a of the motor 56.
So that the eccentric cam 57 comes into contact with the unit housing 5.
And a cam floor 59 attached to a support shaft 58 that projects in the axial direction from one side surface. Then, the eccentric cam 57 is rotated by an angle θ in the ± direction from the reference position X ₀ (θ = 0 °) by the driving force of the steering motor 56, so that a constant cam displacement is obtained.
The drive roll unit housing 51 and, consequently, the drive roll 23 are displaced in the adjustment directions J and K corresponding to the vertical direction by a distance corresponding to the cam displacement amount. The steering mechanism 50 is connected to a control unit (not shown), which controls the home mark detection information of the intermediate transfer belt 21 obtained by the belt home detection device 37 and the belt walk detection device 38 and the belt home detection information. After the walk (meandering) amount of the belt 21 is calculated based on the edge detection information, the steering amount (angle ± α) of the steering mechanism 50 is obtained from the walk amount, and the motor is controlled in accordance with the steering angle ± α. 56 are activated.

By operating the steering mechanism 50 in this way, as shown in FIGS. 3 and 4, the eccentric cam 57 attached to the motor 56 rotates by an angle ± θ corresponding to the angle ± α. The drive roll unit housing 51, one side of which is supported by the eccentric cam 57, and thus one end of the drive roll 23 are displaced in one of the adjustment directions J and K. As a result, the intermediate transfer belt 21 moves along the roll axis to the relatively high end of the drive roll 23, thereby returning to the reference position of the intermediate transfer belt 21 and shifting the belt running state. The minute is corrected.

In the intermediate transfer belt 21, since the drive roll 23 is also used as a steering roll by the steering mechanism 50, the height of the belt 21 is higher than when, for example, the steering mechanism is provided separately and independently. The dimension H can be kept low and the cost can be kept low.

In this intermediate transfer belt 21, FIG.
As shown in the figures, the wrap angle γ of the intermediate transfer belt 21 with the drive roll (steering roll) 23 is increased, so that the grip force is increased and the rotational power of the drive roll 23 is accurately transmitted to the intermediate transfer belt 21. Intermediate transfer belt 2
1 rotates accurately and stably, whereby the alignment of the toner images that are multiplex-transferred from the plurality of photosensitive drums 11 so as to be superimposed on the intermediate transfer belt 21 is also performed favorably. Moreover, the wrap angle γ
Is increased, the displacement of the intermediate transfer belt 21 with respect to the steering operation is promptly performed, and the correction sensitivity of the running deviation of the belt is improved, whereby the direction in which the intermediate transfer belt 21 is perpendicular to the rotation direction B is improved. The rotation of the toner image can be normally performed without any deviation, so that the above-described alignment of the multiple-transferred toner images can be performed well.

Further, in the intermediate transfer belt 21, the first idler roll 24 and the second idler roll 25 sandwich the belt surface 21a of the intermediate transfer belt 21 with which the photosensitive drum 11 of each image forming unit 10 abuts. , Whereby the belt surface 21a is determined. As a result, for example, even when one end of the drive roll 23 is displaced in one of the adjustment directions J and K due to the steering operation described above, as shown in FIG. The displacement of the intermediate transfer belt 21 (the state shown by the dotted line) is absorbed between the backup roller 22 and the first idler roll 24, and therefore, the first idler roll 24 and the second idler roll 25 are particularly absorbed. Is not displaced. As a result, the conditions of the respective primary transfer portions of the plurality of photosensitive drums 11 (the state of contact between the photosensitive drum 11 and the intermediate transfer belt 21 and the like) are all kept the same, so that the primary transfer in each of the primary transfer portions is eventually performed. Is performed satisfactorily and stably.

Further, as shown in FIG. 5A, the tension roll 26 of the intermediate transfer mechanism 20 is provided with a tension applying mechanism 6 using a conventionally known spring member or the like.
0, an arrow M is applied to the intermediate transfer belt 21 from its inner peripheral surface side.
It is a support structure that keeps applying a predetermined tension toward the direction. In addition, as shown in FIG. 5B, one end of the roll shaft 26b to which the roll body 26a is fixed is connected to one of the tension applying mechanisms 60 in order to adjust the degree of deflection of the intermediate transfer belt 21. The roll arm 26b is rotatably and tiltably supported by a spherical bearing 63 with respect to the support arm 61, and the other end of the roll shaft 26b is rotatable with a bearing 64 with respect to the other support arm 62 of the tension applying mechanism 60, and is indicated by arrows. It is supported so as to be displaceable in the M and N directions.

The mechanism for displacing the tension roll 26 is as follows.
Basically, it has substantially the same configuration as the steering mechanism 50. As shown in FIG. 5B, a tension correcting motor 65 such as a stepping motor, an eccentric cam 66 attached to an output shaft 65a of the motor 65, And a cam floor 67 attached to the roll shaft 26b so that the eccentric cam 66 comes into contact with the cam shaft 67. In a similar manner to the case of the steering mechanism 50, the eccentric cam 66 is rotated from the reference position X ₀ (θ = 0 °) by an angle θ in the ± direction (see FIG. 3C), whereby a constant cam displacement is obtained. Thus, the roll shaft 26b and, consequently, the tension roll 26 are displaced in the deflection adjusting directions M and N by a distance corresponding to the cam displacement amount.

The tension roll 26 is provided with a predetermined tension to the intermediate transfer belt 2 so as to be stretched evenly between the plurality of rolls without slack, and the arrows M and N thereof. In this way, the pressing force on the inner peripheral surface of the intermediate transfer belt 21 is adjusted by the displacement in the direction to adjust the bending degree of the belt. The tension roll 26 is provided with a belt end regulating mechanism 70 for suppressing the meandering traveling of the intermediate transfer belt 21. The belt end regulating mechanism 70 includes a donut disc-shaped regulating plate 71 that is loosely fitted to the roll shaft 26b so that the belt end contacts and regulates the end position.
One end is fixed to the regulating plate 71 and the other end is fixed to the support arm 61 to support the first member 1 so that it can be easily and elastically displaced and moved in the axial direction of the roll shaft 26b. . Reference numeral 73 denotes a stopper for stopping the regulating plate 71 at the maximum movement allowable position.

In the intermediate transfer mechanism 20, since the auxiliary roll 26 of the three auxiliary rolls 24 to 26, which is disposed on the end side near the backup roll 22, is configured as a tension roll as described above ( 2), even when the tension correction operation (displacement operation in the directions of arrows M and N) by the roll 26 is performed, as shown in FIG. The displacement of the transfer belt 21 (the state shown by the dotted line) is absorbed between the second idler roll 25 and the pre-roll 27 (or the backup roll 22 if the roll 27 is not provided). Photosensitive drum 1 determined between first idler roll 24 and second idler roll 25
There is no displacement of the belt surface 21a with which the belt 1 contacts. As a result, all the conditions of the primary transfer portions of the plurality of photosensitive drums 11 are kept the same, so that the primary transfer in each of the primary transfer portions can be performed satisfactorily and stably.

In the intermediate transfer mechanism 20, the pre-roll 27 is provided between the tension roll 26 and the backup roll 22 as described above,
As shown in FIG. 7, the approach angle δ of the intermediate transfer belt 21 to the secondary transfer section (the required angle with respect to the entry line of the recording sheet P to the secondary transfer section) is determined. Thereby, even if the above-described operation of adjusting the deflection of the tension roll 26 is performed, for example, the displacement of the intermediate transfer belt 21 accompanying the displacement of the tension roll 26 (shown by a dotted line) as shown in FIG. State) is absorbed between the pre-roll 27 and the intermediate transfer belt 21 that passes through the pre-roll 27 and enters the secondary transfer unit without being affected by the displacement of the tension roll 26. Kept in state. As a result, the situation (entrance angle δ) of the secondary transfer section is constant, so that the above-described secondary transfer can be performed satisfactorily and stably.

According to the image forming apparatus of the first embodiment,
The increase in apparatus height due to the provision of the intermediate transfer mechanism 20 is extremely small, and the apparatus height can be reduced despite the use of the intermediate transfer method. Also,
The intermediate transfer mechanism 20 corrects the deviation of the running of the intermediate transfer belt 20 and adjusts the degree of deflection to ensure stable rotation without slack, and the photosensitive drum 11 on the intermediate transfer belt 21 by the correcting operation and the adjusting operation. Therefore, even when a full-color image is formed, high-quality images free from image defects such as color misregistration and color unevenness due to the poor running state of the intermediate transfer belt 21 can be obtained even when a full-color image is formed. A color image is obtained.

[Embodiment 2] FIG. 8 shows an intermediate transfer mechanism 20 according to a second embodiment of the present invention.
In the image forming apparatus according to the second embodiment, a first idler roll 24 and a tension roll 28 are provided as auxiliary rolls of the intermediate transfer mechanism 20 according to the first embodiment, and the tension roll 28 is supported between the first idler roll 24 and the roll 24. Arrows Q, within a reference plane S (two-dot chain line) having the same positional relationship as the belt surface (belt surface with which the photosensitive drum 11 contacts) 21a
Embodiment 1 except that it is configured to be displaced in the R direction.
Has the same configuration as the image forming apparatus according to the first embodiment.

The mechanism for displacing the tension roll 28 in the intermediate transfer mechanism 20 can be basically the same as that in the first embodiment (FIG. 5B), and the only displacement direction is the direction of the arrows Q and R. It may be changed so that Further, the tension roll 28 is supported by a tension applying mechanism 60 similarly to the tension roll 26 of the first embodiment, whereby the predetermined tension is continuously applied to the intermediate transfer belt 21.

In the intermediate transfer mechanism 20 according to the second embodiment, as shown in FIG. 8, the tension roll 28 is displaced in the directions of arrows Q and R along the reference surface S, whereby the deflection of the intermediate transfer belt 21 is performed. Is adjusted.
When adjusting the deflection, the tension roll 2
8 is displaced within the reference surface S, the belt surface 21a with which the photosensitive drum 11 contacts is not displaced in the vertical direction or the like with the displacement of the roll, and the tension roll 28 and the first idler roll 24 It is kept constant while supported in between. As a result, all the conditions of the primary transfer portions of the plurality of photosensitive drums 11 are kept the same, so that the primary transfer in each of the primary transfer portions can be performed satisfactorily and stably.

Even when the tension roll 28 is displaced in the directions of arrows Q and R during the deflection adjustment, as shown in FIG. 9, the tension roll 28 and the secondary transfer backup roll 22 If the same pre-roll 27 as in the first embodiment is provided, the entry angle δ of the intermediate transfer belt 21 to the secondary transfer portion is kept constant, and stable secondary transfer is secured.

[Other Embodiments] In the first and second embodiments, as the tension rolls 26, 28 capable of adjusting the deflection of the intermediate transfer belt 21, auxiliary rolls provided at the end side on the backup roll 22 side are used. Although the case where the auxiliary roll (24) is used is exemplified, the auxiliary roll (24) disposed at the end on the drive roll 22 side may be used as the tension roll. However, from the viewpoint of reliably avoiding fluctuations in the rotation speed of the intermediate transfer belt 21 in the primary transfer unit by the operation of adjusting the deflection of the tension roll, as in Embodiments 1 and 2, the backup roll 2
It is desirable that the auxiliary rolls disposed at the two ends be used as tension rolls.

[0053]

As described above, according to the image forming apparatus of the present invention, as described above, the intermediate transfer belt is stretched by a main roll or the like so as to be elongated and flat, and is inserted into the apparatus main body. Since it is arranged in a substantially horizontal state, the height dimension of the entire intermediate transfer belt in a state of being stretched on a roll is suppressed as much as possible, and the height of the apparatus by disposing the intermediate transfer belt is reduced. The increase can be minimized. As a result, despite the fact that the image forming apparatus employs the intermediate transfer method, the height of the entire apparatus can be reduced. Further, since the intermediate transfer belt is stretched in a flat state as described above, and the belt is appropriately provided with an auxiliary roll and a functional roll, the intermediate transfer belt rotates extremely stably. A good intermediate transfer operation can be performed without impairing the original performance required of the belt.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic diagram illustrating a main part of an intermediate transfer mechanism according to the first embodiment.

3A is a side view of a main part showing a configuration of a driving roll and a steering mechanism, FIG. 3B is a cross-sectional view taken along line BB of FIG. 3A, and FIG. 3C is a main part of an eccentric cam mechanism. FIG.

FIG. 4A is a perspective view of a main part showing a state of a steering operation of a drive roll, and FIG. 4B is an explanatory view showing a behavior state of an intermediate transfer belt during the steering operation.

5A is a schematic view showing a tension roll tension applying mechanism, and FIG. 5B is a cross-sectional view of a main part showing a tension roll displacement mechanism.

FIG. 6 is an explanatory diagram illustrating a behavior state of an intermediate transfer belt during a deflection adjusting operation of a tension roll.

FIG. 7 is an explanatory view of a main part showing a function of a pre-roll.

FIG. 8 is a schematic diagram illustrating a main part of an intermediate transfer mechanism according to a second embodiment.

FIG. 9 is an explanatory view of a main part showing a function of a pre-roll in the intermediate transfer mechanism of FIG. 7;

FIG. 10A is a schematic diagram showing a typical example of an image forming apparatus using a conventional intermediate transfer drum, and FIG. 10B is a schematic diagram showing a typical example of an image forming apparatus using a conventional intermediate transfer belt.

FIG. 11 is a schematic view showing another example of a conventional image forming apparatus using an intermediate transfer belt.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Device main body, 11 ... Photosensitive drum (image carrier), 21 ...
Intermediate transfer belt, 21a: belt surface on which the photosensitive drum contacts, 22: backup roll (main roll), 23
... Driving roll and steering roll (main roll), 24, 25 ... Idler roll (auxiliary roll), 2
6, 28: tension roll (auxiliary roll), 27: pre-roll, P: recording sheet (transfer material), S: reference plane,
H: height dimension of the entire belt, δ: belt entry angle.

Claims (7)

[Claims] An endless intermediate transfer belt stretched around at least two main rolls and rotated in a fixed direction, and a toner image formed on an image carrier is primarily transferred to the intermediate transfer belt. An apparatus for forming an image by secondary-transferring the toner image to a material to be transferred later, wherein the intermediate transfer belt is installed such that its longitudinal direction is substantially horizontal in the apparatus main body, and An image forming apparatus, wherein one of the two main rolls is used as a secondary transfer backup roll to constitute a part of a secondary transfer section. 2. The apparatus according to claim 1, wherein the other main roll that is not the secondary transfer backup roll is:
It is used as a drive roll that transmits rotational power to the intermediate transfer belt, and at the same time, is used as a steering roll that displaces the entire roll and corrects a traveling deviation in a direction perpendicular to the rotation direction of the intermediate transfer belt. Image forming device. 3. The apparatus according to claim 2, wherein an intermediate transfer belt is supported between the driving roll and the secondary transfer backup roll from the inner peripheral surface side thereof, and a belt surface on which the image carrier abuts is provided. An image forming apparatus, comprising: at least two auxiliary rolls to be fixed. 4. The apparatus according to claim 3, wherein one of the at least two auxiliary rolls provided at both ends applies tension to the intermediate transfer belt and carries the image on the intermediate transfer belt. An image forming apparatus, wherein the image forming apparatus is used as a tension roll that is displaced within a reference plane having the same positional relationship as a belt surface with which a body abuts to adjust deflection of an intermediate transfer belt. 5. The apparatus according to claim 3, wherein three or more auxiliary rolls are provided, and one of the auxiliary rolls provided at both ends is used to apply tension to the intermediate transfer belt and to apply the tension to the intermediate transfer belt. An image forming apparatus, wherein the image forming apparatus is used as a tension roll that adjusts the deflection of the intermediate transfer belt by displacing the pressing force on the intermediate transfer belt surface in a direction of increasing or decreasing the pressing force. 6. The device according to claim 4, wherein
An image forming apparatus characterized in that an auxiliary roll disposed on an end side serving as a secondary transfer backup roll side is used as a tension roll. 7. The apparatus according to claim 6, wherein an intermediate transfer belt is supported between the backup roll for secondary transfer and the tension roll from an inner peripheral surface side thereof, and the belt advance angle to the secondary transfer portion is adjusted. An image forming apparatus comprising a pre-roll to be determined.