Image forming device

Abstract

The present invention provides an image forming device. The image forming device comprises: a belt that conveys a toner image while holding it on the front side; a back support portion that presses the back side of the belt and rotates about a first rotation axis, thereby bending the belt into a shape that protrudes toward the front side; a transfer portion that sandwiches the belt between the back support portion and rotates about a second rotation axis, pressing a conveyed sheet of paper against the belt to transfer the toner image on the belt to the sheet of paper; a guide portion that guides the conveyed sheet of paper to an area sandwiched between the belt and the transfer portion; and a guide control portion that controls the position or posture of the guide portion such that the thinner the sheet of paper being guided, the closer the sheet contact point is to the first rotation axis with respect to a reference direction, wherein the sheet contact point is the point where the leading end of the conveyed sheet of paper contacts the belt, and the reference direction is the direction from the second rotation axis toward the first rotation axis.

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus. Background Art

[0002] Image forming apparatuses that utilize a belt known as an intermediate transfer belt are known. In this type of image forming apparatus, a toner image on the belt is transferred to a conveyed sheet of paper. Regarding the conveyance of the paper, various structures have been proposed for guiding the paper along a predetermined path.

[0003] For example, Japanese Patent Application Laid-Open No. 2009-196803, Japanese Patent Application Laid-Open No. 2013-015551, and Japanese Patent Application Laid-Open No. 2016-004129 are cited as prior art documents. Summary of the Invention

[0004] In the above-mentioned image forming apparatus, when transferring the toner image on the belt to the conveyed paper, if the transferred paper is so-called thin paper, there is a risk that the paper may stick to the belt and deviate from the predetermined conveyance path.

[0005] An object of the present disclosure is to provide an image forming apparatus that reduces the risk of paper and a belt sticking together after transfer, regardless of the thickness of the paper.

[0006] According to a first embodiment of the present disclosure, an image forming apparatus is provided, comprising: a belt that holds and conveys a toner image on the front side; a back support portion that presses the back side of the belt and rotates around a first rotation axis to bend the belt into a shape that protrudes toward the front side; a transfer portion that rotates around a second rotation axis while sandwiching the belt with the back support portion, pushing a conveyed sheet of paper onto the belt to transfer the toner image on the belt onto the sheet of paper; a guide portion that guides the conveyed sheet of paper to an area sandwiched between the belt and the transfer portion; and a guide control portion that controls the position or posture of the guide portion in the following manner: the thinner the thickness of the guided sheet of paper, the closer the sheet contact point is to the first rotation axis with respect to a reference direction, the sheet contact point being a point at which the front end of the conveyed sheet of paper contacts the belt, and the reference direction being a direction from the second rotation axis toward the first rotation axis.

[0007] According to the second embodiment of the present disclosure, when guiding a paper thinner than a predetermined reference thickness, the guide control unit controls the position or posture of the guide unit in the following manner: the paper contact point is closer to the first rotation axis with respect to the reference direction than when guiding a paper thicker than the reference thickness.

[0008] According to the third scheme of the present disclosure, the image forming device has a pressure control unit, which controls the pushing pressure of the transfer unit on the belt by moving the transfer unit in the direction of contact or separation with the belt, and the guide control unit controls the position or posture of the guide unit in conjunction with the movement control of the transfer unit by the pressure control unit.

[0009] According to the fourth aspect of the present disclosure, the guide control unit is connected to the pressure control unit, and controls the guide unit by a power source that is common to the movement control of the transfer unit.

[0010] According to the fifth aspect of the present disclosure, the guide control unit is connected to the pressure control unit via the transfer unit.

[0011] According to the sixth scheme of the present disclosure, the image forming device has a cleaning section, which contacts the transfer section to clean the transfer section, and the position or posture of the cleaning section changes as the pressure control section controls the movement of the transfer section. The cleaning section is the guide control section, and the guide section changes its position or posture according to the change of the position or posture of the cleaning section as the pressure control section controls the movement of the transfer section.

[0012] According to the seventh aspect of the present disclosure, at least the surface of the cleaning portion that contacts the transfer portion is formed of an elastic body.

[0013] According to an eighth aspect of the present disclosure, the elastic body is composed of sponge.

[0014] According to the ninth aspect of the present disclosure, the guide control unit changes the paper contact point with respect to the reference direction by controlling the position of the guide unit in the reference direction.

[0015] According to the tenth aspect of the present disclosure, the guide control portion changes the paper contact point with respect to the reference direction by controlling the inclination angle of the guide portion with respect to the reference direction.

[0016] According to the 11th scheme of the present disclosure, an image forming device is provided, which comprises: a belt that holds a colorant image on the front side while conveying it; a back support portion that contacts the back side of the belt and supports the back side; a transfer portion that rotates around a second rotation axis while sandwiching the belt between the belt and the back support portion, pushing the conveyed paper onto the belt and transferring the colorant image on the belt onto the paper; a guide portion that guides the conveyed paper to a transfer area sandwiched by the belt and the transfer portion; and a guide control portion that controls the position or posture of the guide portion in the following manner: the thinner the thickness of the paper guided by the guide portion, the more the discharge angle of the paper discharged from the transfer area changes in a direction away from the belt.

[0017] (Effect)

[0018] According to the first and eleventh aspects of the disclosure, the risk of the transferred paper and the tape sticking together is reduced regardless of the thickness of the paper.

[0019] According to the second aspect of the disclosure, the position or posture of the guide portion is switched depending on whether the thickness of the paper is thinner or thicker than the reference thickness.

[0020] According to the third aspect of the disclosure, both the pressing pressure of the transfer section on the belt and the position or posture of the guide section are controlled according to the thickness of the paper.

[0021] According to the fourth and fifth aspects of the disclosure, the driving source becomes simpler than when control is performed by a separate driving source.

[0022] According to the sixth aspect of the disclosure, the position or posture of the guide portion changes in accordance with changes in the position or posture of the cleaning portion accompanying the movement control of the transfer portion.

[0023] According to the seventh and eighth aspects of the disclosure, scratching of the transfer portion due to contact of the cleaning portion is suppressed.

[0024] According to the ninth aspect of the disclosure, the risk of the transferred paper and the belt sticking together is reduced by controlling the position of the guide portion.

[0025] According to the tenth aspect of the disclosure, the risk of the transferred paper and the belt sticking together is reduced by controlling the posture of the guide portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a structural diagram showing one embodiment of the image forming apparatus of the present disclosure.

[0027] Figure 2 It shows Figure 1 Schematic diagram of the structure of the secondary transfer portion of the image forming apparatus shown.

[0028] Figure 3 It shows Figure 1 Schematic diagrams of a third example (A) and a fourth example (B) of the structure of the secondary transfer portion of the image forming apparatus shown. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0030] Figure 1 This is a structural diagram showing one embodiment of the image forming apparatus of the present disclosure.

[0031] Figure 1The image forming apparatus 1 shown is a tandem-type color printer comprising image forming units 10Y, 10M, 10C, and 10K for yellow (Y), magenta (M), cyan (C), and black (K) arranged side by side. In addition to printing monochrome images, it can also print full-color images composed of four-color toner images. Toner cartridges 18Y, 18M, 18C, and 18K contain toners for the Y, M, C, and K colors.

[0032] Since the four image forming units 10Y, 10M, 10C, and 10K have substantially the same structure, the yellow image forming unit 10Y will be used as a representative example for description. The image forming unit 10Y includes a photosensitive drum 11Y, a charging device 12Y, an exposure device 13Y, a developing device 14Y, a primary transfer roller 15Y, and a photoreceptor cleaner 16Y. The photosensitive drum 11Y, charging device 12Y, and developing device 14Y in the image forming unit 10Y are housed in a process cartridge CR. The process cartridge CR is detachably mounted to the main body 1H of the image forming apparatus 1.

[0033] The photoreceptor drum 11Y has a photosensitive layer provided on its cylindrical surface, holds an image formed on the surface, and rotates in the direction of arrow A, which is the direction around the axis of the cylinder. The charging device 12Y, exposure device 13Y, developing device 14Y, primary transfer roller 15Y, and photoreceptor cleaner 16Y are arranged around the photoreceptor drum 11Y in this order in the direction of arrow A.

[0034] The charging device 12Y charges the surface of the photosensitive drum 11Y. In this embodiment, the charging device 12Y is a charging roller that contacts the surface of the photosensitive drum 11Y. A voltage is applied to the charging device 12Y, charging the surface of the photosensitive drum 11Y in contact therewith. The exposure device 13Y exposes the surface of the photosensitive drum 11Y with exposure light, forming an electrostatic latent image on the surface of the photosensitive drum 11Y. The exposure device 13Y emits laser light corresponding to image data supplied from outside the image forming apparatus 1, and uses this laser light to scan the photosensitive drum 11Y.

[0035] The developing device 14Y includes a developing roller 141 that rotates in the direction of arrow C. This developing roller 141 transports the developer within the developing device 14Y to a developing position facing the photosensitive drum 11Y. At this developing position, the developer transported to the developing position is used to develop the electrostatic latent image formed on the surface of the photosensitive drum 11Y, forming an unfixed toner image on the surface of the photosensitive drum 11Y. Toner is supplied to the developing device 14Y from a toner cartridge 18Y. The developing device 14Y stirs the developer, which is a mixture of magnetic carrier and toner, to charge the toner and magnetic carrier. The charged toner then develops the electrostatic latent image on the photosensitive drum 11Y. The primary transfer roller 15Y is a roller that faces the photosensitive drum 11Y, sandwiching the intermediate transfer belt 30.

[0036] The primary transfer roller 15Y applies a voltage to the photosensitive drum 11Y, thereby transferring the toner image on the photosensitive drum 11Y to the intermediate transfer belt 30 .

[0037] The photoconductor cleaner 16Y cleans the surface of the photoconductor drum 11Y by removing unnecessary substances such as toner remaining on the photoconductor drum 11Y after transfer.

[0038] The image forming apparatus 1 also includes a control unit 1A, a UI (user interface) 1B, an intermediate transfer belt 30, a fixing unit 60, and a paper conveying unit 80. The control unit 1A is responsible for controlling the entire image forming apparatus 1. The control unit 1A is a type of information processing device that has the function of executing various programs. By executing control programs in the control unit 1A, the various parts of the image forming apparatus 1 are controlled. In addition, the control unit 1A has the function of receiving image data transmitted from an external device of the image forming apparatus 1, such as a personal computer (hereinafter abbreviated as "PC"). In the image forming apparatus 1, an image based on the received image data is formed on paper under the control of the control unit 1A.

[0039] The UI 1B includes a display screen, push buttons, etc., and is responsible for exchanging information between the image forming apparatus 1 and the user. The UI 1B may be formed of a touch panel.

[0040] The intermediate transfer belt 30 is an endless belt stretched over belt support rollers 31 to 35 including a support roller 34. The intermediate transfer belt 30 circulates in the direction of arrow B along a travel path passing through the image forming units 10Y, 10M, 10C, and 10K and the secondary transfer unit T2. Toner images of various colors are transferred from the image forming units 10Y, 10M, 10C, and 10K to the intermediate transfer belt 30. The intermediate transfer belt 30 moves while holding these toner images of various colors.

[0041] In the secondary transfer section T2, a secondary transfer roller 50 is located opposite the backup roller 34, sandwiching the intermediate transfer belt 30. This secondary transfer roller 50 rotates while sandwiching the intermediate transfer belt 30 and the paper P between it and the backup roller 34, one of the belt backup rollers 31 to 35. The surface of the secondary transfer roller 50 is made of an elastic material, and the secondary transfer roller 50 is pressed against the intermediate transfer belt 30, forming a nip region where the secondary transfer roller 50 and the intermediate transfer belt 30 come into contact. In the secondary transfer section T2, the paper P is sandwiched in this nip region, and a voltage of opposite polarity to the charged polarity of the toner is applied, thereby transferring the toner image on the intermediate transfer belt 30 to the paper P.

[0042] The fixing unit 60 fixes the toner image onto the paper P. The fixing unit 60 includes a heating roller 61 and a pressure roller 62, with a heater disposed within the heating roller 61. The heating roller 61 and the pressure roller 62 each hold the unfixed toner image before fixing. The heating roller 61 and the pressure roller 62 rotate in directions that further convey the conveyed paper P. The heating roller 61 and the pressure roller 62 sandwich the paper P between them, heating and pressurizing it. In this manner, the unfixed toner image is fixed to the paper P in the fixing unit 60, and the paper P is then fed downstream in the conveyance direction.

[0043] The paper conveying unit 80 includes a take-out roller 81 for removing paper P from the paper container T; a conveying roller 82 for conveying the removed paper P; a registration roller 84 for feeding the paper P toward the secondary transfer unit T2, where the secondary transfer roller 50 is located; and a discharge roller 86 for discharging the paper P to the outside. The paper conveying unit 80 conveys the paper P along a paper conveyance path R that passes through the secondary transfer unit T2 and the fixing unit 60. Information about the paper P, i.e., its thickness, is pre-entered in the image forming apparatus 1, based on the name of the paper P stored in the paper container T, such as plain paper or thick paper. Specifically, plain paper is registered as a default value. If another type of paper P is stored in the paper container T, the user operates the UI 1B to input the type of paper P stored in the paper container T. This information about the type of paper P is stored in the control unit 1A.

[0044] The image forming apparatus 1 also includes a density sensor 71 for measuring the density of the toner image on the intermediate transfer belt 30, and a line sensor 72 for measuring the density of the image on the paper P that has passed through the fixing unit 60. In the image forming apparatus 1, during an image non-formation period (when an image is not formed based on image data received from a PC or the like), a toner patch is formed on the intermediate transfer belt 30, and the density of the toner patch is measured by the density sensor 71. This measured data is transmitted to the control unit 1A, which adjusts the density of the image formed based on the image data received from the PC or the like.

[0045] The line sensor 72 has a structure in which multiple sensors are arranged in the paper width direction (main scanning direction). The line sensor 72 is used to monitor the image formed on the paper P passing through its position. The line sensor 72 measures the density and other characteristics of the image formed on the paper P. The measured data is transmitted to the control unit 1A, which monitors whether the image has a density and color within the reference range.

[0046] right Figure 1 The basic operation of the image forming apparatus 1 shown in FIG.

[0047] In the yellow image forming unit 10Y, the photosensitive drum 11Y is driven to rotate in the direction of arrow A, and the surface of the photosensitive drum 11Y is charged by the charging device 12Y. The exposure device 13Y irradiates the photosensitive drum 11Y with exposure light corresponding to the data corresponding to each color in the image data. The exposure device 13Y forms an electrostatic latent image on the surface of the photosensitive drum 11Y by irradiating the surface of the photosensitive drum 11Y with exposure light based on the image data corresponding to yellow in the image data supplied from the outside. Yellow toner is supplied from the toner cartridge 18Y to the developing device 14Y. The developing device 14Y develops the electrostatic latent image on the photosensitive drum 11Y with the toner to form a toner image. The photosensitive drum 11Y rotates while retaining the yellow toner image formed on its surface. The toner image formed on the surface of the photosensitive drum 11Y is transferred to the intermediate transfer belt 30 by the primary transfer roller 15Y. The toner remaining on the photoconductor drum 11Y after the transfer is removed by the photoconductor cleaner 16Y.

[0048] The intermediate transfer belt 30 circulates in the direction of arrow B. The image forming units 10M, 10C, and 10K corresponding to colors other than yellow form toner images corresponding to the respective colors, similarly to the image forming unit 10Y, and transfer the toner images of the respective colors to the intermediate transfer belt 30 by overlapping them with the toner image transferred by the image forming unit 10Y.

[0049] The paper P is removed from the paper container T by the take-out roller 81. The paper P is conveyed along the paper conveyance path R in the direction indicated by arrow C toward the secondary transfer section T2 by the conveying roller 82 and the registration roller 84. The registration roller 84 feeds the paper P into the secondary transfer section T2 based on the timing of the toner image transfer onto the intermediate transfer belt 30. The secondary transfer section T2 transfers the toner image from the intermediate transfer belt 30 onto the paper P. The paper P, with the toner image transferred onto it, is conveyed from the secondary transfer section T2 to the fixing section 60, where the toner image transferred onto the paper P is fixed to the paper P. This forms an image on the paper P. The image-formed paper P is further conveyed while the image formed on the paper P is read by the line sensor 72, and is discharged to the outside of the image forming apparatus 1 by the discharge roller 86. Toner remaining on the intermediate transfer belt 30 after transfer in the secondary transfer section T2 is removed by the belt cleaner 90.

[0050] Figure 2 It shows Figure 1 Schematic diagram of the structure of the secondary transfer portion of the image forming device shown in FIG. Figure 2 (A) Figure 2 (B) is a first example of the structure of the secondary transfer unit. Figure 2 (A) shows the operation when the paper container T contains plain paper or paper P with a thickness less than that of plain paper. Figure 2 (B) shows the operation when the paper container T contains paper P having a thickness exceeding that of ordinary paper. Figure 2 (C) is a second example of the structure of the secondary transfer unit. This will be described after the first example.

[0051] In the secondary transfer section T2, the backup roller 34 and the secondary transfer roller 50 face each other, sandwiching the intermediate transfer belt 30. The backup roller 34 presses the back surface of the intermediate transfer belt 30, which faces the front surface holding the toner image, causing the intermediate transfer belt 30 to be bent so as to protrude toward the front side, thereby rotating about the rotation axis 341. Furthermore, the secondary transfer roller 50 is a roller that functions as follows: sandwiching the intermediate transfer belt 30 between the secondary transfer roller 50 and the backup roller 34, rotating about the rotation axis 501, pressing the conveyed paper P against the intermediate transfer belt 30, and transferring the toner image on the intermediate transfer belt 30 onto the paper P. Here, the intermediate transfer belt 30 is an example of a belt in this disclosure. Furthermore, the backup roller 34 is an example of a back surface support portion in this disclosure, and its rotation axis 431 is an example of a first rotation axis in this disclosure. The secondary transfer roller 50 corresponds to an example of a transfer unit in the present disclosure, and the rotation shaft 501 thereof corresponds to an example of a second rotation shaft in the present disclosure.

[0052] Furthermore, a guide member 85 and a cleaning member 86 are provided immediately upstream of the secondary transfer section T2 in the paper transport direction. The guide member 85 guides the transported paper P to the nip region between the intermediate transfer belt 30 and the secondary transfer roller 50. Furthermore, the cleaning member 86 contacts the secondary transfer roller 50 to clean it. At least the surface 861 of the cleaning member 86 that contacts the secondary transfer roller 50 is made of an elastic material. In this embodiment, it is specifically formed of a sponge 863 attached to a support plate 862.

[0053] The secondary transfer roller 50 is rotatably supported by a support member 51 via a bearing (not shown). Furthermore, the support member 51 is pressed by a cam member 52 to freely move up and down, and is lifted upward by the cam member 52. The cam member 52 is rotated by a motor 53, causing the support member 51 to move up and down according to the rotation angle of the cam member 52.

[0054] Furthermore, the guide member 85 and the cleaning member 86 are fixed to another support member 87. Furthermore, the support member 87 is rotatable around a rotation shaft 871.

[0055] Here, Figure 2 (A) shows the Figure 1 The paper container T shown in the figure contains plain paper or paper P with a thickness less than that of plain paper and forms an image on the paper P. Figure 2 (B) shows a case where a sheet P made of thick paper having a predetermined thickness or thicker than regular paper is accommodated in the sheet container T and an image is formed on the sheet P.

[0056] Compare Figure 2 (A) and Figure 2 (B), the cam member 52 rotates 180 degrees, Figure 2 In the case of (A), the support member 51 supporting the rotation shaft 501 of the secondary transfer roller 50 is lifted upward as indicated by the arrow U. This means that the secondary transfer roller 50 is strongly pressed by the intermediate transfer belt 30, thereby expanding the nip region.

[0057] And, in Figure 2 In (A), the cleaning member 86 is pressed by the secondary transfer roller 50. Figure 2 Compared with (B), the support member 87 rotates around the rotation axis 871 in the direction of arrow R. Along with this, the guide member 85 and the cleaning member 86 fixed to the support member 87 also rotate in the direction of arrow R.

[0058] Here, the direction from the rotation shaft 501 of the secondary transfer roller 50 toward the rotation shaft 341 of the backup roller 34 is Figure 2The direction indicated by the arrow L is set as the reference direction. Next, focus on the paper contact point W where the leading end of the conveyed paper contacts the intermediate transfer belt 30. Figure 2 (A) and Figure 2 (B), in Figure 2 In the case of (A), the paper contact point W is close to the rotation axis 341 of the support roller 34 with respect to the reference direction.

[0059] In the case of thin paper P, there is a higher risk that the paper P will not follow the predetermined conveying path and will stick to the intermediate transfer belt 30 after leaving the nip region between the intermediate transfer belt 30 and the secondary transfer roller 50, compared to thick paper. Figure 2 (A) Figure 2 As shown by the angles θ1 and θ2 (θ1>θ2) in (B), the paper P that has escaped the nip area tends to move further away from the intermediate transfer belt 30 as the paper contact point W approaches the rotation axis 34 of the support roller 34. Furthermore, under the same conditions such as thickness, the further the paper P tends to move away from the intermediate transfer belt 30, the lower the risk of the paper P sticking to the intermediate transfer belt 30.

[0060] On the other hand, in the case of thick paper, if the nip pressure, which is the pressing force for pressing the secondary transfer roller 50 to the intermediate transfer belt 30, is high, the impact when the paper protrudes into the nip area is large, and there is a possibility of causing disadvantages such as colorant image disorder. In the case of thick paper P, it is preferable to lower the nip pressure than in the case of ordinary paper or paper P with a thickness less than ordinary paper.

[0061] Here, by adjusting the nip pressure, the position of the guide member 85 is changed to adjust the paper contact point W for paper P of plain paper or a thickness less than plain paper and paper P made of thick paper.

[0062] Thus, the secondary transfer portion T2 suitable for various types of paper from thin paper to thick paper is configured.

[0063] exist Figure 2 (A) Figure 2 In the first example shown in (B), the posture of the guide member 85, that is, the inclination angle relative to the reference direction L, is controlled by changing the posture of the cleaning member 86 pressed by the secondary transfer roller 50. Therefore, in this first example, the cleaning member 86 can be considered as an example of the guide control unit referred to in this disclosure. Alternatively, the combination of the motor 53, the cam member 52, the secondary transfer roller 50, and the cleaning member 86 can be considered as an example of the guide control unit referred to in this disclosure.

[0064] Furthermore, the cam member 52 and the motor 53 move the secondary transfer roller 50 toward the intermediate transfer belt 30 to control the pressing pressure of the secondary transfer roller 50 against the intermediate transfer belt 30, which corresponds to an example of the pressure control unit referred to in this disclosure. Furthermore, in this first example, the cleaning member 86, which is an example of the guide control unit, controls the posture of the guide member 85 in conjunction with the movement control of the secondary transfer member 50 by the cam member 52 and the motor 53, which is an example of the pressure control unit.

[0065] Furthermore, in the case of this first example, the cleaning component 86, which is an example of a guide control unit, is connected to the cam component 52 and the motor 53, which are equivalent to an example of a pressure control unit, by means of the secondary transfer roller 50, and the guide component 85 is controlled by the motor 53, which is a power source shared with the movement control of the secondary transfer roller 50.

[0066] While the example described here uses two stages of control for paper P: plain paper or paper P thinner than plain paper, and paper P thicker than plain paper and thicker than plain paper, but for example, the guide member 85 may be controlled in three stages: thin paper thinner than plain paper, plain paper, and thick paper, such that the thinner the paper, the closer the paper contact point W is to the rotation axis 341 of the support roller 34 with respect to the reference direction L. Alternatively, rather than providing two or three stages, the guide member 85 may be controlled in such a manner that the thinner the paper, the closer the paper contact point W is to the rotation axis 341 of the support roller 34. These points also apply to the second and subsequent examples described below.

[0067] exist Figure 2 In the second example shown in (C), a support member 87, to which the guide member 85 and the cleaning member 86 are fixed, is supported by a support post 88 so as to be movable vertically. Then, as the cam member 52 rotates and the secondary transfer roller 50 moves vertically, pressing the cleaning member 86, the support member 87 moves vertically along the support post 88. This vertical movement also causes the guide member 85 to move vertically, adjusting the paper contact point W. Adjustment of the paper contact point W can be achieved by adjusting the inclination angle of the guide member 85, as in the first example, or by adjusting the height of the guide member 85, as in this second example.

[0068] Figure 3 It shows Figure 1 Schematic diagrams of a third example (A) and a fourth example (B) of the structure of the secondary transfer portion of the image forming apparatus shown.

[0069] exist Figure 3In the case of the third example shown in (A), the supporting member 55 includes both the rotating shaft 501 supporting the secondary transfer roller 50 and the guide member 85. Here, since the cleaning member 86 is not required when controlling the position or posture of the guide member 85 (see Figure 2 ), the cleaning member 86 is not shown. However, the cleaning member 86 may be supported by the support member 55. The rotation of the cam member 52 causes the support member 55 to move the rotating shaft 501 of the secondary transfer roller 50 vertically, and the guide member 85 also moves vertically with this rotation. This adjusts the paper contact point W.

[0070] And, in Figure 3 In the case of the fourth example shown in (B), the following structure is set: the supporting part 51 for supporting the rotating shaft 501 of the secondary transfer roller 50 and the supporting part 87 for supporting the guide part 85 are independently provided, and the cam parts 52 and 90 provided corresponding to the supporting parts 51 and 85 are driven by the motors 53 and 89, so that the vertical movement of the rotating shaft 501 of the secondary transfer roller 50 and the vertical movement or rotation of the guide part 85 are linked and driven.

[0071] In this manner, the secondary transfer roller 50 and the guide member 85 may be driven in conjunction with each other by separate driving sources.

[0072] In the case of this fourth example, the motor 89 and the cam member 90 on the guide member 85 side correspond to an example of a guide control unit referred to in the present disclosure.

Claims

1. An image forming apparatus comprising: a belt that conveys the toner image while holding it on the front side; a back support portion that presses the back surface of the belt and rotates around a first rotation axis to bend the belt into a shape that protrudes toward the front side; a transfer section that sandwiches the belt between itself and the back support section and rotates about a second rotation axis, pressing a conveyed sheet of paper against the belt to transfer the toner image on the belt to the paper; a guide portion that guides the conveyed paper to an area sandwiched between the belt and the transfer portion; a guide control unit configured to control a position or posture of the guide unit such that the thinner the guided paper, the closer the paper contact point is to the first rotation axis with respect to a reference direction, wherein the paper contact point is a point where the leading end of the conveyed paper contacts the belt, and the reference direction is a direction from the second rotation axis toward the first rotation axis; a pressure control unit that controls a pressing pressure of the transfer unit against the belt by moving the transfer unit in a direction of contact with or separation from the belt; and a cleaning unit that contacts the transfer unit to clean the transfer unit, wherein a position or posture of the cleaning unit changes as the pressure control unit controls the movement of the transfer unit; The guide control unit controls the position or posture of the guide unit in conjunction with the pressure control unit's control of the transfer unit. The cleaning section is the guide control section, and the guide section changes a position or posture according to a change in the position or posture of the cleaning section accompanying the movement control of the transfer section by the pressure control section.

2. The image forming apparatus according to claim 1, wherein When guiding paper thinner than a predetermined reference thickness, the guide control unit controls the position or posture of the guide unit so that the paper contact point is closer to the first rotation axis with respect to the reference direction than when guiding paper thicker than the reference thickness.

3. The image forming apparatus according to claim 1, wherein The guide control unit is connected to the pressure control unit, and controls the guide unit using a power source that is common to movement control of the transfer unit.

4. The image forming apparatus according to claim 3, wherein The guide control unit is connected to the pressure control unit via the transfer unit.

5. The image forming apparatus according to claim 1, wherein At least a surface of the cleaning portion that contacts the transfer portion is formed of an elastic body.

6. The image forming apparatus according to claim 5, wherein The elastic body is composed of sponge.

7. The image forming apparatus according to any one of claims 1 to 6, wherein: The guide control unit changes the paper contact point with respect to the reference direction by controlling the position of the guide unit in the reference direction.

8. The image forming apparatus according to any one of claims 1 to 6, wherein: The guide control portion changes the paper contact point with respect to the reference direction by controlling an inclination angle of the guide portion with respect to the reference direction.

9. An image forming apparatus comprising: a belt that conveys the toner image while holding it on the front side; a back surface supporting portion that contacts the back surface of the belt to support the back surface; a transfer section that sandwiches the belt between itself and the back support section and rotates about a second rotation axis, pressing a conveyed sheet of paper against the belt to transfer the toner image on the belt to the paper; a guide portion that guides the conveyed paper to a transfer area sandwiched between the belt and the transfer portion; as well as a guide control unit configured to control a position or posture of the guide unit so that a discharge angle of the paper discharged from the transfer area changes in a direction away from the belt as the thickness of the paper guided by the guide unit becomes thinner; a pressure control unit that moves the transfer unit in a direction of contact with or separation from the belt to control a pressing pressure of the transfer unit on the belt; as well as a cleaning unit that contacts the transfer unit to clean the transfer unit, wherein a position or posture of the cleaning unit changes as the pressure control unit controls the movement of the transfer unit; The guide control unit controls the position or posture of the guide unit in conjunction with the pressure control unit's control of the transfer unit. The cleaning section is the guide control section, and the guide section changes a position or posture according to a change in the position or posture of the cleaning section accompanying the movement control of the transfer section by the pressure control section.

Images