Transfer belt device and image forming apparatus

Abstract

To prevent meandering of an intermediate transfer belt to allow image formation with good image quality.SOLUTION: An intermediate transfer belt device 20 has an intermediate transfer belt 21, a driving roller 22 that drives the intermediate transfer belt 21, and a pressing roller 24 that presses from an outer surface of the intermediate transfer belt 21 toward the driving roller 22. The pressing roller 24 is disposed at a position corresponding to a downstream end in a rotation direction C in a contact area α of the intermediate transfer belt 21 and the driving roller 22. The intermediate transfer belt 21 is in contact with the pressing roller 24 and is provided such that the outer surface of the intermediate transfer belt 21 is wound around an outer surface of the pressing roller 24 at a predetermined winding angle θ.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an intermediate transfer belt device and an image forming apparatus equipped with the intermediate transfer belt device. [Background technology]

[0002] Some electrophotographic image forming devices use an intermediate transfer system in which toner images are transferred from multiple image carriers to an intermediate transfer belt in a sequentially overlapping manner, and then the toner images are transferred from the intermediate transfer belt to a sheet in a secondary transfer. In this type of image forming device, if the intermediate transfer belt meanders, it adversely affects the image quality during image formation, so it is necessary to suppress such meandering.

[0003] In addition, in order to improve the ease of peeling the sheet from the intermediate transfer belt, the diameter of the drive roller that drives the intermediate transfer belt is sometimes reduced, but the reduced diameter drive roller has a reduced gripping force on the intermediate transfer belt, making the intermediate transfer belt more susceptible to slipping.

[0004] For example, Patent Document 1 discloses that a pressure roller having three rollers with different outer diameters is provided downstream of a process section in the direction of movement of the conveyor belt and upstream of two sensors that detect marks on the conveyor belt, to press the conveyor belt against a drive roller and suppress slippage. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-210363 A Summary of the Invention [Problem to be solved by the invention]

[0006] As disclosed in the above-mentioned Patent Document 1, even if a pressure roller is provided facing the drive roller in the middle of the contact area between the drive roller and the conveyor belt, if the rotation axes of the rollers including the drive roller are not arranged parallel to each other, an axial force that causes the conveyor belt to be biased will be generated. Therefore, even if slippage can be suppressed to some extent, the conveyor belt will be biased, causing a problem that the amount of meandering of the conveyor belt will increase.

[0007] In addition, in the case of a drive roller with a small diameter, the influence of the mounting angle and outer diameter tolerance of the drive roller becomes even greater, so that the intermediate transfer belt is more likely to become biased, and there is a risk of the amount of meandering increasing.

[0008] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide an intermediate transfer belt device and an image forming apparatus which can suppress meandering of the intermediate transfer belt and enable the formation of images of good quality, even if the diameter of the drive roller that drives the intermediate transfer belt is reduced. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the intermediate transfer belt device of the present invention comprises an intermediate transfer belt, a drive roller arranged to abut against the inner surface of the intermediate transfer belt and drive the intermediate transfer belt, and a pressing member that presses the outer surface of the intermediate transfer belt toward the drive roller, the pressing member being disposed at a position corresponding to the downstream end of the intermediate transfer belt in the rotational direction in the contact area between the intermediate transfer belt and the drive roller, the intermediate transfer belt abutting against the pressing member, and the outer surface of the intermediate transfer belt being wrapped around the outer surface of the pressing member at a predetermined winding angle.

[0010] More specifically, the intermediate transfer belt device may have the following configuration: The pressing member is a roller member, and the winding angle of the intermediate transfer belt with respect to the pressing member is preferably within 90 degrees.

[0011] In the intermediate transfer belt device having the above-described configuration, it is preferable that the pressing member is a roller member and is rotationally driven via a drive gear. In this case, it is preferable that the pressing member is rotationally driven faster than the drive roller with a predetermined speed difference relative to the drive roller.

[0012] In the intermediate transfer belt device having the above configuration, it is preferable that the drive roller is rotatably supported by a support member, and the support member is provided with a bearing engagement portion that engages with a bearing portion of the pressing member so that the rotation axis of the pressing member and the rotation axis of the drive roller are parallel to each other.

[0013] In the intermediate transfer belt device having the above-mentioned structure, it is preferable that the pressing member has an outer surface covered with a coating layer made of an elastic member.

[0014] Further, an image forming apparatus having an intermediate transfer belt device having the above-mentioned configuration is also within the scope of the technical concept of the present invention.

[0015] As a result, even if the diameter of the drive roller that drives the intermediate transfer belt is reduced, meandering of the intermediate transfer belt can be suppressed, making it possible to form images with good quality. Effect of the Invention

[0016] According to the present invention, even if the diameter of the drive roller for driving the intermediate transfer belt is reduced, meandering of the intermediate transfer belt can be suppressed, and images of good quality can be formed. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic front view showing an image forming apparatus according to an embodiment of the present invention; [Diagram 2] FIG. 2 is an explanatory diagram that illustrates a schematic diagram of an intermediate transfer belt device (at rest) according to an embodiment of the present invention. [Diagram 3] FIG. 2 is an explanatory diagram that illustrates a schematic diagram of an intermediate transfer belt device (when driven) according to an embodiment of the present invention. [Figure 4] 4 is an explanatory diagram illustrating a schematic configuration of a drive roller side in the intermediate transfer belt device illustrated in FIG. 3. [Diagram 5] 11 is an explanatory diagram showing the belt tension acting on the intermediate transfer belt when the intermediate transfer belt is stationary in an intermediate transfer belt device as a reference example. FIG. [Figure 6] 6 is an explanatory diagram showing the belt tension acting on the intermediate transfer belt when the intermediate transfer belt is driven in an intermediate transfer belt device as a reference example. FIG. [Figure 7] FIG. 7 is a simplified explanatory diagram showing the belt tension during driving shown in FIG. 6. [Figure 8] 5 is a simplified explanatory diagram showing belt tension during driving of an intermediate transfer belt in an intermediate transfer belt device according to an embodiment of the present invention; FIG. [Figure 9] 4 is an enlarged explanatory diagram showing a support structure for a pressure roller provided in the intermediate transfer belt device; FIG. [Figure 10] FIG. 4 is an enlarged explanatory view showing a driving mechanism of the pressure roller. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] An intermediate transfer belt device 20 according to an embodiment of the present invention and an image forming apparatus 1 including the intermediate transfer belt device 20 will be described with reference to the drawings.

[0019] (Overall configuration of image forming apparatus) FIG. 1 is a schematic front view showing an image forming apparatus 1 according to an embodiment of the present invention.

[0020] The image forming apparatus 1 is a multifunction machine having, for example, a scanner function, a copier function, a printer function, and a facsimile function, and transmits an image of an original document read by an image reading device 18 to the outside, and forms an image of the read original document or an image received from the outside on a sheet in color or monochrome. This image forming apparatus 1 includes a charging device 15, an optical scanning device 11, a developing device 12, a photoconductor drum 13, a drum cleaning device 14, a paper feeding device 17, an image reading device 18, an intermediate transfer belt device 20, a fixing device 44, and the like.

[0021] The image forming apparatus 1 handles image data corresponding to color images using the colors black (K), cyan (C), magenta (M), and yellow (Y), or monochrome images using a single color (e.g., black). The image reading device 18 reads an original document or an original document conveyed from an original document conveying section (ADF) to generate image data. The image transfer section 10 of the image forming apparatus 1 is provided with four developing devices 12, four photoconductor drums 13, four drum cleaning devices 14, and four charging devices 15 for forming four types of toner images, and four image stations Pa, Pb, Pc, and Pd are configured so that the developing devices 12, Pb, Pc, and Pd correspond to black, cyan, magenta, and yellow, respectively.

[0022] The drum cleaning device 14 removes and collects residual toner on the surface of the photoreceptor drum 13. The charging device 15 charges the surface of the photoreceptor drum 13. The optical scanning device 11 exposes the surface of the photoreceptor drum 13 to light to form an electrostatic latent image. The developing device 12 develops the electrostatic latent image on the surface of the photoreceptor drum 13 to form a toner image on the surface of the photoreceptor drum 13. Through this series of operations, a toner image of each color is formed on the surface of each photoreceptor drum 13.

[0023] An intermediate transfer belt device 20 is provided above the photosensitive drums 13, and an intermediate transfer roller 26 is disposed with an intermediate transfer belt 21 interposed therebetween. The intermediate transfer belt 21 is an image carrier on which a toner image is formed, and is stretched around a drive roller 22 and a tension roller 23 to rotate (circularly move) in the direction of arrow C. The tension roller 23 is provided to apply a predetermined tension to the intermediate transfer belt 21. The toner images of each color formed on the surface of each photosensitive drum 13 are sequentially transferred (primary transfer) onto the intermediate transfer belt 21 and overlapped, thereby forming a color toner image on the surface of the intermediate transfer belt 21. A detailed configuration of this intermediate transfer belt device 20 will be described later.

[0024] A nip area (secondary transfer position) is formed between the secondary transfer roller 43 of the secondary transfer section 42 and the intermediate transfer belt 21, and the sheet conveyed through the sheet conveying path 31 is sandwiched in the nip area and conveyed. When the sheet passes through the nip area, the toner image on the surface of the intermediate transfer belt 21 is transferred to the sheet, and the sheet is conveyed to the fixing device 44. The toner and the like remaining on the intermediate transfer belt 21 are collected by the belt cleaning device 41.

[0025] The fixing device 44 includes a fixing roller 45 and a pressure roller 46 which rotate while sandwiching the sheet. The fixing device 44 sandwiches the sheet, on which the toner image has been transferred, between the fixing roller 45 and the pressure roller 46 and applies heat and pressure to fix the toner image to the sheet.

[0026] The paper feeder 17 stores sheets used for image formation, and is provided below the optical scanning device 11. The sheet is pulled out from the paper feeder 17 by a pickup roller 33, transported through a sheet transport path 31, and transported to a paper output tray 37 via a secondary transfer unit 42 and a fixing device 44 via a paper output roller 36. Various pairs of rollers are arranged in the sheet transport path 31, such as a registration roller 35 that temporarily stops the sheet, aligns the leading edge of the sheet, and then starts transporting the sheet in accordance with the transfer timing of a color toner image in a nip area between the intermediate transfer belt 21 and the secondary transfer roller 43, a plurality of transport rollers 34 that promote the transport of the sheet, and a paper output roller 36.

[0027] When an image is to be formed on the back side as well as the front side of the sheet, the sheet is transported in the reverse direction from the discharge rollers 36 to the sheet reversing transport path 32 to invert the sheet, and the sheet is guided again to the registration rollers 35, where an image is formed on the back side in the same manner as on the front side, and the sheet is transported to the discharge tray 37.

[0028] (Intermediate transfer belt device) The intermediate transfer belt device 20 is an endless belt supported by a main body frame (not shown) that is installed facing the ends of the intermediate transfer belt 21 in the width direction. As shown in Fig. 1, a tension roller 23 and a drive roller 22 are axially supported in parallel to each other on the left side X1 and right side X2 in the left-right direction X. Furthermore, four intermediate transfer rollers 26 corresponding to each color are disposed between the tension roller 23 and the drive roller 22, each axially supported by the main body frame at both ends in the axial direction.

[0029] 2 and 3 are explanatory diagrams that show the intermediate transfer belt device 20, with Fig. 2 showing the intermediate transfer belt 21 at rest (when not forming an image) and Fig. 3 showing the intermediate transfer belt 21 at drive (when forming a color image). The X direction in the figures corresponds to the left-right direction when the image forming apparatus 1 is viewed from the front (see Fig. 1), with X1 indicating the left side and X2 indicating the right side, and the Y direction in the figures corresponds to the front-rear direction when the image forming apparatus 1 is viewed from the front, with Y1 indicating the front side and Y2 indicating the rear side. Thus, while the image forming apparatus 1 in Fig. 1 is shown as viewed from the front side Y1, Figs. 2 and 3 show the state as viewed from the rear side Y2 of Fig. 1.

[0030] 2, when viewed from the rear side Y2, photoconductor drums 13 corresponding to four image stations Pa, Pb, Pc, and Pd are disposed along the outer surface of the intermediate transfer belt 21. In addition, intermediate transfer rollers 26 are disposed at positions corresponding to the photoconductor drums 13, with the intermediate transfer belt 21 in between. In the illustrated embodiment, the intermediate transfer belt 21 is disposed above the four photoconductor drums 13.

[0031] The intermediate transfer rollers 26 are provided so as to be capable of coming into contact with and being separated from the opposing photosensitive drums 13. This allows the intermediate transfer rollers 26 to be displaced between a position where the intermediate transfer belt 21 is pressed against the opposing photosensitive drums 13 from the inner surface side, and a position where the intermediate transfer belt 21 is separated from the opposing photosensitive drums 13. As shown in FIG. 2, when no image is being formed, all of the intermediate transfer rollers 26 are disposed at the separated positions, so that the intermediate transfer belt 21 is disposed at a predetermined position separated from all of the photosensitive drums 13.

[0032] In the color image forming apparatus, which is the image forming apparatus 1 shown in the exemplary embodiment, the intermediate transfer roller 26 is configured to be displaced according to each operating state during monochrome image formation, color image formation, and non-image formation. For example, the intermediate transfer belt 21 is separated from all the photoconductor drums 13 as shown in Fig. 2 during non-image formation, and contacts only the black photoconductor drum 13 during monochrome image formation. During color image formation, all the intermediate transfer rollers 26 are disposed at their respective pressing positions, so that the intermediate transfer belt 21 is disposed in contact with all the photoconductor drums 13 as shown in Fig. 3.

[0033] A suspension roller 25 is disposed near the drive roller 22 for driving the intermediate transfer belt 21. The intermediate transfer belt 21 is wound around the drive roller 22 and the suspension roller 25 at its end on the right side X2. Each roller, such as the drive roller 22 and the suspension roller 25, applies a predetermined belt tension to the intermediate transfer belt 21.

[0034] The intermediate transfer belt device 20 is also provided with a meandering correction mechanism (not shown) for mechanically correcting meandering (deviation) of the intermediate transfer belt 21 caused by misalignment of the parallelism of the rotation axes of the drive roller 21, tension roller 23, suspension roller 25, etc. that suspend the intermediate transfer belt 21 due to installation errors, differences in thermal expansion of the installation parts caused by environmental temperature changes, etc. The meandering correction mechanism is provided on the tension roller 23 and includes a deviation transmission member that moves along the axial direction of the tension roller 23 due to the deviation force of the intermediate transfer belt 21 generated along the axial direction of the tension roller 23 (in this case, the front-rear direction Y). The meandering correction mechanism is configured to automatically adjust the deviation force generated in the intermediate transfer belt 21 by mechanically changing the inclination of the rotation axis direction of the tension roller 23 according to the amount of movement of the deviation transmission member along the axial direction, thereby suppressing meandering of the intermediate transfer belt 21.

[0035] In the intermediate transfer belt device 20 according to the present embodiment, the driving roller 22 has a smaller diameter than the conventional one, and the intermediate transfer belt 21 is more likely to meander. Therefore, the meandering correction mechanism increases the amount of change in the inclination of the rotation axis of the tension roller 23 to correct the meandering of the intermediate transfer belt 21, which may result in the meandering correction mechanism becoming larger. Therefore, in order to suppress the slippage of the intermediate transfer belt 21 relative to the driving roller 22 and to minimize the amount of meandering that occurs in the intermediate transfer belt 21, the driving roller 22, which has the greatest influence on the bias force of the intermediate transfer belt 21 due to its characteristic of transmitting a rotational force to the intermediate transfer belt 21, is provided with a pressing member as described below.

[0036] (Pressing member) Fig. 4 is an explanatory diagram that illustrates a schematic configuration of the drive roller 22 side (right side X2 portion) of the intermediate transfer belt device 20 illustrated in Fig. 3. In Fig. 4, the intermediate transfer belt 21 is configured to move in a rotation direction C by the rotation drive of the drive roller 22 in a rotation direction D.

[0037] The intermediate transfer belt device 20 is provided with a pressing member that presses the outer surface of the intermediate transfer belt 21 against the drive roller 22. As this pressing member, a pressing roller 24 that is a roller member in this embodiment is provided.

[0038] 4, the intermediate transfer belt 21 and the drive roller 22 are provided in contact with each other in a contact area α. The pressure roller 24 is disposed in contact with the outer surface of the intermediate transfer belt 21 at a position in the contact area α corresponding to the downstream end Pe of the intermediate transfer belt 21 in the rotation direction C. The intermediate transfer belt 21 is provided in contact with the pressure roller 24 and the outer surface of the intermediate transfer belt 21 is wound around the outer surface of the pressure roller 24 at a predetermined winding angle θ. The winding angle θ of the intermediate transfer belt 21 with respect to the pressure roller 24 is set to be within 90 degrees.

[0039] Belt tension is generated in the intermediate transfer belt 21 which is in contact with the driving roller 22 at the contact area α. Here, the belt tension in the intermediate transfer belt 21 will be briefly described.

[0040] Fig. 5 shows the belt tension acting on the intermediate transfer belt 21 when it is stationary (when no image is formed) in an intermediate transfer belt device as a reference example, and Fig. 6 is an explanatory diagram showing the belt tension acting on the intermediate transfer belt 21 when it is driven (when an image is formed). In these examples, similar to Fig. 4, the image forming apparatus 1 is shown as seen from the rear side Y2, and the pressing roller 24 is not provided.

[0041] 5, when the intermediate transfer belt 21 is stationary, the action of the tension roller 23 generates belt tensions T1 and T2 at both ends of the contact area α between the intermediate transfer belt 21 and the drive roller 22. In this manner, when the intermediate transfer belt 21 is stationary, the belt tension T1 acting on the upstream end of the intermediate transfer belt 21 in the rotation direction C at the contact area α is approximately equal to the belt tension T2 acting on the downstream end of the intermediate transfer belt 21 in the rotation direction C. In addition, when considering an intermediate transfer belt 21 of a very small length including the base point P0, the belt tension T1 and its reaction force T 11 A balance between the tangential component force and the radial component force F of the driving roller 22 is formed.

[0042] On the other hand, as shown in Fig. 6, when the intermediate transfer belt 21 is driven, that is, when the driving roller 22 rotates in the rotation direction D, a belt tension T3 acts on the upstream end of the contact area α where the intermediate transfer belt 21 contacts the driving roller 22 in the rotation direction C, and a belt tension T4 acts on the downstream end of the contact area α in the rotation direction C, where the belt tension T4 is smaller than the belt tension T3. The reason for this is explained below. In the state shown in Fig. 6, as shown in Fig. 3, the intermediate transfer belt 21 is in contact with the photosensitive drums 13 facing the intermediate transfer roller 26, and this acts as a rotation load. Therefore, the belt tension acting on the intermediate transfer belt 21 is somewhat tight on the upstream side of the contact area α between the intermediate transfer belt 21 and the driving roller 22, and is somewhat loose on the downstream side of the contact area α.

[0043] Here, if the intermediate transfer belt 21 in the contact area α is divided into, for example, four equally divided infinitesimal length areas, and the radial component of the force acting on each infinitesimal length area is defined as a component of the force (F), each component of the force (F) gradually decreases from the upstream side to the downstream side of the contact area α due to the influence of the belt tension acting on the intermediate transfer belt 21. That is, in the contact area α, a radial component of the force F1 acts on the upstream side of the rotation direction C of the intermediate transfer belt 21, while this force gradually decreases toward the downstream side, becoming components of the force F2, the force F3, and the force F4.

[0044] Fig. 7 is an explanatory diagram showing in a simplified manner the direction of movement of the intermediate transfer belt 22 when it receives the belt tension and each component force (F) during driving shown in Fig. 6, and for simplification, the contact area α is shown as 180 degrees. In Fig. 7, the right side of the figure shows the drive roller 22 as seen from the back side Y2, and the left side of the figure shows the drive roller 22 as seen from the right side X2.

[0045] As shown in the figure, a belt tension Tp acts on the upstream end of the intermediate transfer belt 21 in the rotation direction C, and a belt tension Tr acts on the downstream end of the rotation direction C. The belt tension Tp at the upstream end is greater than the belt tension Tr at the downstream end by a tension difference ΔT. This is because a rotation load (intermediate transfer roller 26, photosensitive drum 13) is connected to the upstream side in the rotation direction C, and the intermediate transfer belt 21 receives this load during rotation. Therefore, as described above, when considering the contact area α as a small length equally divided by 45 degrees, the radial component force (F) acting on the intermediate transfer belt 21 gradually decreases from the upstream side to the downstream side of the contact area α, and becomes the component force F1, the component force F2, the component force F3, and the component force F4 in that order from the upstream side in the rotation direction C. The sum of these component forces F1, F2, F3, and F4 (which are frictional forces acting from the drive roller 21 on the intermediate transfer belt 22) enables the intermediate transfer belt 21 to be rotated without slipping, even when the intermediate transfer rollers 26 and the photosensitive drums 13 arranged upstream of the rotational direction of the drive roller 21 are in contact with the intermediate transfer belt 21.

[0046] More specifically, the component force F1 at the base point P1 is a friction force μF1 (μ is a friction coefficient) acting between the intermediate transfer belt 21 and the drive roller 22, and the component force F3 at the base point P3 is a friction force μF3. Here, when the axial direction of the rotation axis (rotation axis line 22a) of the drive roller 22 is not perpendicular to the left-right direction X parallel to the rotation direction C of the intermediate transfer belt 21 and is shifted, that is, when the rotation axis of the drive roller 22 is shifted to the right X2 on the back side Y2 and to the left X1 on the front side Y1, as shown on the left side of FIG. 7, the friction forces (μF1, μF3) acting on the intermediate transfer belt 21 act to move the intermediate transfer belt 21 in a direction shifted from the rotation direction D of the drive roller 22. The direction of movement changes depending on the position (P1, P2, P3, P4) of the drive roller 22 in the rotation direction D.

[0047] 7, at base point P1 located on the upstream side of the rotation direction C, the frictional force μF1 does not act as a force along the rotation direction D, but acts as a force inclined toward the front side Y1 diagonally with respect to the rotation direction D. Also, at base point P3 located on the downstream side of the rotation direction C, the frictional force μF3 acts as a force inclined toward the back side Y2 diagonally with respect to the rotation direction D.

[0048] The frictional force between the intermediate transfer belt 21 and the drive roller 22, which is generated at an angle with respect to the rotational direction D of the drive roller 22, is a factor in causing the intermediate transfer belt 21 to be biased. The frictional force due to the upstream force components F1 and F2 acts in the front side Y1 direction, and the frictional force due to the downstream force components F3 and F4 acts in the back side Y2 direction. In this case, since the force components F1 and F2 are larger than the force components F3 and F4, they are significantly affected by the frictional force in the front side Y1 direction, causing the intermediate transfer belt 21 to be biased in the front side Y1 direction.

[0049] Therefore, if the rotation axis (rotation axis 22a) of the drive roller 22 is misaligned even slightly with respect to the arrangement of the rotation axes of other rollers provided in the intermediate transfer belt device 20, the frictional force between the intermediate transfer belt 21 and the drive roller 22 will not be along the rotation direction D of the drive roller 22, but will be generated in a direction shifted in the front-rear direction Y. As a result, the intermediate transfer belt 21 will be easily misaligned in the front-rear direction Y and will tend to meander. Furthermore, when the drive roller 22 is a roller with a small diameter as shown in this embodiment, this tendency becomes more pronounced, and the difference between the force components F1 to F4 becomes larger, so it is considered that the bias will be more likely to occur.

[0050] To address this problem, the intermediate transfer belt device 20 according to this embodiment is configured to suppress bias in the intermediate transfer belt 21 and minimize the amount of meandering by providing a pressure roller 24 that presses the outer surface of the intermediate transfer belt 21 against the drive roller 22, as shown in FIG. 4.

[0051] Fig. 8 is a simplified explanatory diagram of the belt tension when the intermediate transfer belt 21 is driven when the pressing roller 24 is provided, and is a diagram equivalent to Fig. 7. The contact area α is shown as 180 degrees for simplification. In Fig. 8 as well, the right side of the figure shows the drive roller 22 as seen from the back side Y2, and the left side of the figure shows the drive roller 22 as seen from the right side X2. As in the above, it is assumed that there is an axial deviation in the rotation axis of the drive roller 22, and for example, the rotation axis of the drive roller 22 is shifted to the right side X2 on the back side Y2 and to the left side X1 on the front side Y1.

[0052] 8, the pressure roller 24 is disposed at the downstream end of the contact area α, and is provided so that the outer surface of the intermediate transfer belt 21 is wrapped around the outer surface of the pressure roller 24 at a predetermined wrapping angle θ. The pressure roller 24 is provided in contact with the outer surface of the intermediate transfer belt 21 so as to press it.

[0053] Considering a minute length corresponding to the winding angle θ of the intermediate transfer belt 21, at the base point P5, a component force F5 acts on the intermediate transfer belt 21 in the radial direction of the pressure roller 24. Therefore, as shown on the left side of Fig. 8, in the upstream region A1 of the rotation direction C of the intermediate transfer belt 21 with respect to the rotation direction D of the drive roller 22, the frictional forces due to the components F1 and F2 act with an inclination toward the front side Y1, whereas in the downstream region A2, the frictional forces due to the components F3 to F5 act with an inclination toward the back side Y2. In other words, compared to the configuration without the pressure roller 24 shown in Fig. 7, in the configuration with the pressure roller 24 shown in Fig. 8, a frictional force μF5 due to the component force F5 further acts on the intermediate transfer belt 21.

[0054] By providing the pressing roller 24, the intermediate transfer belt device 20 can increase the frictional force in the downstream region A2 by adding the component force F5 to the components force F3 and F4 in the downstream region A2 even if the rotation shaft of the drive roller 22 is misaligned in the axial direction. Therefore, it is possible to increase the frictional force in the direction opposite to the deviation direction (in this case, the front side Y1 direction) that may occur in the intermediate transfer belt 21 on the drive roller 22 (in this case, the back side Y2 direction). That is, in this case, the frictional force in the downstream region A2 can resist the deviation in the front side Y1 direction caused by the frictional force in the upstream region A1, and the influences of these are offset by the frictional force occurring in the opposite direction, making it possible to reduce the amount of deviation.

[0055] It is preferable that the wrap angle θ of the intermediate transfer belt 21 with respect to the pressure roller 24 is 90 degrees or less. If the wrap angle θ exceeds 90 degrees, the radial component force F5 generated by the pressure roller 24 cannot act as a frictional force in the opposite direction to the deviation direction of the upstream region A1, and the effect of the pressure roller 24 is considered to be reduced. By setting the wrap angle θ of the intermediate transfer belt 21 with respect to the pressure roller 24 to 90 degrees or less, in the case shown in FIG. 8, the deviation of the intermediate transfer belt 21 occurring in the front side Y1 direction can be pulled back to the opposite direction, the back side Y2 direction, and the deviation of the intermediate transfer belt 21 occurring as a whole can be kept small.

[0056] Furthermore, the reduced diameter of the drive roller 22 causes problems such as a decrease in gripping force on the intermediate transfer belt 21 and an increase in the effect of the mounting angle and outer diameter tolerance of the drive roller 22, but the provision of the pressure roller 24 makes it possible to reduce the deviation of the intermediate transfer belt 21 as described above. This makes it possible to effectively suppress meandering of the intermediate transfer belt 21, and also reduces the load on the meandering correction mechanism.

[0057] As a more specific configuration of the pressure roller 24, for example, a coating layer 242 made of an elastic material is preferably provided on the outer circumferential surface of a cylindrical metal core material. The coating layer 242 is provided to have a uniform thickness all around the pressure roller 24, and the elastic material constituting this coating layer 242 is preferably a rubber-based material such as EPDM (ethylene-propylene-diene rubber).

[0058] Fig. 9 is an enlarged explanatory diagram showing the support structure of the pressure roller 24, and Fig. 10 is an enlarged explanatory diagram showing the drive mechanism of the pressure roller 24. Figs. 9 and 10 show a schematic configuration of the right side X2 portion of the intermediate transfer belt device 20 when viewed from the rear side Y2.

[0059] 9, in the intermediate transfer belt device 20, the drive roller 22 has a rotation shaft 221 rotatably supported by a support member 27. The support member 27 is supported by the main body side frame or the like.

[0060] The pressure roller 24 has a bearing portion 244 of a rotating shaft 241 held by a bearing holder portion 245. Similarly, the secondary transfer roller 43 has a bearing portion 432 of its rotating shaft 431 held by a bearing holder portion 433. Both the pressure roller 24 and the secondary transfer roller 43 are disposed facing the drive roller 22. The pressure roller 24 is provided with a biasing member (spring member) 246 in the bearing holder portion 245, which biases the pressure roller 24 in a direction pressing the pressure roller against the drive roller 22. The secondary transfer roller 43 is also provided with a biasing member 434 in the bearing holder portion 433, which biases the pressure roller 24 in a direction pressing the pressure roller against the drive roller 22. As a result, the pressure roller 24 and the secondary transfer roller 43 are provided while being biased toward the drive roller 22.

[0061] The support member 27 is provided with a first bearing engagement portion 271 that engages with the bearing holder portion 245 of the pressure roller 24 so that the rotation shaft 241 of the pressure roller 24 and the rotation shaft 221 of the drive roller 22 are parallel to each other. As shown in Fig. 9, the first bearing engagement portion 271 is formed by cutting out a part of the upper end portion of the support member 27 so as to support the bearing holder portion 245.

[0062] Further, the support member 27 is provided with a second bearing engagement portion 272 that engages with the bearing holder portion 433 of the secondary transfer roller 43. The second bearing engagement portion 272 is formed by cutting out a part of a side portion of the support member 27 in an arrangement form facing the first bearing engagement portion 271 so as to support the bearing holder portion 433. As a result, the rotation shaft 241 of the pressure roller 24 and the rotation shaft 431 of the secondary transfer roller 43 are positioned parallel to each other with respect to the rotation shaft 221 of the drive roller 22 rotatably supported by the support member 27, and are stably supported.

[0063] 10, the pressing roller 24 may be configured to be rotationally driven via a gear 243. The driving force of the driving roller 22 is transmitted to the rotating shaft 221 via a gear 222, and the pressing roller 24 is rotationally driven in a rotation direction D. In contrast, the pressing roller 24 includes a gear 243 that meshes with the gear 222 of the driving roller 22, and the driving force is transmitted to the rotating shaft 241 via the gear 243, and the pressing roller 24 is rotationally driven in a rotation direction E. This allows the pressing roller 24 to rotate without slipping, and can effectively act on the intermediate transfer belt 21.

[0064] In addition, it is preferable to set the gear ratio of the gears 222, 243 and the outer diameters of the pressure roller 24 and the drive roller 22 so that the rotation speed of the pressure roller 24 is faster than that of the drive roller 22. This allows the pressure roller 24 to be rotated faster than the drive roller 22 at a predetermined speed difference with respect to the drive roller 22, and can more effectively suppress deviation of the intermediate transfer belt 21. The speed difference between the rotation speed of the pressure roller 24 and the rotation speed of the drive roller 22 can be appropriately adjusted, and even a slight difference of about 0.2 to 1% can sufficiently suppress deviation.

[0065] In the intermediate transfer belt device 20 configured as above, even if the driving roller 22 has a small diameter, the intermediate transfer belt 21 can be rotated without slipping because the pressure roller 24 is provided, and even if the rotation shaft 221 of the driving roller 22 is misaligned, the pressure roller 24 can be made to act so as to reduce the deviation occurring in the intermediate transfer belt 21. Therefore, it is possible to effectively suppress meandering of the intermediate transfer belt 21, and also to reduce the load on the meandering correction mechanism.

[0066] In the above embodiment, the pressure roller 24 is not limited to the configuration including the gear 243, and may be configured to be wound around the outer surface of the intermediate transfer belt 21 and rotate by frictional force between the intermediate transfer belt 21. The pressure roller 24 may have any other configuration as long as it is disposed at a position corresponding to the downstream end of the intermediate transfer belt 21 in the rotation direction C of the intermediate transfer belt 21 in the contact area α between the intermediate transfer belt 21 and the drive roller 22, and the intermediate transfer belt 21 is wound around the pressure roller 24 at a winding angle θ of 90 degrees or less.

[0067] The image forming apparatus 1 equipped with the intermediate transfer belt device 20 as described above is not limited to the multifunction machine shown in FIG. 1, but can be applied to various image forming apparatuses. The above-disclosed embodiment is merely illustrative in all respects and does not provide a basis for a restrictive interpretation. Therefore, the technical scope of the present invention is not interpreted only by the above-disclosed embodiment, but is defined based on the claims. Also, all modifications within the meaning and scope equivalent to the claims are included. [Explanation of symbols]

[0068] 1. Image forming device 10 Image transfer section 11 Optical scanning device 12 Developing device 13 Photoconductor drum 20 Intermediate transfer belt device 21 Intermediate transfer belt 22 Drive roller 22a Rotation axis of the drive roller 23 Tension roller 24 Pressure roller (pressure member) 241 Rotational Axis 242 Covering layer 243 Gear 244 Bearing section 245 Bearing holder part (bearing part) 246 Pressing member 25 Suspension roller 26 Intermediate transfer roller 27 Support member 271 First bearing engagement portion (bearing engagement portion) 272 Second bearing engagement part 42 Secondary transfer section 43 Secondary transfer roller

Claims

1. An intermediate transfer belt onto whose outer surface a toner image is transferred; a drive roller disposed in contact with an inner surface of the intermediate transfer belt to drive the intermediate transfer belt; a pressing member that presses the outer surface of the intermediate transfer belt against the drive roller; a secondary transfer roller that transfers the toner image transferred onto the outer surface of the intermediate transfer belt onto a sheet; the pressing member is disposed at a position corresponding to a downstream end of the intermediate transfer belt in a rotation direction of the intermediate transfer belt in a contact area between the intermediate transfer belt and the drive roller, the secondary transfer roller is disposed at an upstream end of the contact area in a rotation direction of the intermediate transfer belt, the pressing member and the secondary transfer roller are both disposed opposite the drive roller, a pressing member that presses the intermediate transfer belt against the pressing member; and an outer surface of the intermediate transfer belt is wound around the outer surface of the pressing member at a predetermined winding angle.

2. 2. The transfer belt device according to claim 1, 2. A transfer belt device according to claim 1, wherein the pressing member is a roller member, and the winding angle of the intermediate transfer belt with respect to the pressing member is set to 90 degrees or less.

3. 3. The transfer belt device according to claim 1, The transfer belt device according to the present invention is characterized in that the pressing member is a roller member, and is rotationally driven via a drive gear.

4. 4. The transfer belt device according to claim 3, The transfer belt device according to the present invention is characterized in that the pressing member is rotated faster than the driving roller by a predetermined speed difference with respect to the driving roller.

5. 5. The transfer belt device according to claim 3, The drive roller is rotatably supported by a support member, a bearing engaging portion of the support member that engages with a bearing portion of the pressing member such that a rotation axis of the pressing member and a rotation axis of the drive roller are parallel to each other;

6. In the transfer belt device according to any one of claims 1 to 5, The transfer belt device according to claim 1, wherein the pressing member has an outer surface covered with a coating layer that is made of an elastic material.

7. 7. An image forming apparatus comprising the transfer belt device according to claim 1.

Images