Secondary transfer device and image forming device

Abstract

To provide a secondary transfer device and an image forming apparatus that can improve the performance of a decompression mechanism and improve the separability of a recording medium.SOLUTION: A secondary transfer device comprises a secondary transfer roller 41, a crimping mechanism, a decompression mechanism, and a support member. The secondary transfer roller 41 forms a transfer nip. The crimping mechanism applies a nip pressure between the secondary transfer roller 41 and a counter roller 28. When a leading end and a rear end of a recording medium pass through the transfer nip, the decompression mechanism temporarily reduces the nip pressure. The support member 32 supports the secondary transfer roller 41 so that it can change the position in a conveyance direction of the recording medium.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a secondary transfer device and an image forming apparatus. [Background technology]

[0002] An image forming apparatus has an image forming unit that forms an image on a recording medium, and forms an image on the recording medium using the image forming unit based on output job information. In the image forming unit, a photoconductor is first charged and the charge is erased in accordance with the original image, i.e., exposure, to form an electrostatic latent image. Toner is then attached to the electrostatic latent image on the photoconductor using a developing unit. The toner attached to the photoconductor is then transferred to an intermediate transfer belt, and the toner image transferred to the intermediate transfer belt is secondarily transferred to a recording medium such as paper using a secondary transfer device. The transferred toner image is then fixed to the recording medium using a fixing device, forming an image on the recording medium.

[0003] At the secondary transfer position, the opposing roller that stretches the intermediate transfer belt and the secondary transfer roller of the secondary transfer device sandwich the intermediate transfer belt between them, forming a transfer nip. The load changes significantly when the leading edge of the recording medium enters the transfer nip or when the trailing edge of the recording medium leaves the transfer nip. This can cause fluctuations in the rotation speed of the intermediate transfer belt or vibrations, resulting in streaks or unevenness in the image.

[0004] A technology for mitigating the impact when the leading or trailing edge of such a recording medium passes through the transfer nip is described, for example, in Patent Document 1. Patent Document 1 describes a technology that includes a pressure release unit that displaces the secondary transfer roller between a pressing position where it presses the intermediate transfer belt across an opposing roller and a separated position where it is separated from the intermediate transfer belt. Patent Document 1 also describes a technology that includes a high-speed pressure reduction unit that temporarily reduces the nip pressure created by the secondary transfer roller in the pressing position when the leading or trailing edge of the paper passes through. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-183991 Summary of the Invention [Problem to be solved by the invention]

[0006] Furthermore, in order to improve the separation of the recording medium from the intermediate transfer belt, the secondary transfer roller is positioned inside the intermediate transfer belt relative to the normal line of the opposing roller to the intermediate transfer belt, i.e., upstream in the transport direction. However, when the secondary transfer roller is positioned inside the intermediate transfer belt, there is a problem in that the secondary transfer roller separates from the intermediate transfer belt during decompression, changing the tension of the intermediate transfer belt and causing fluctuations in the speed at which the intermediate transfer belt rotates.

[0007] In view of the above-mentioned conventional problems, an object of the present invention is to provide a secondary transfer device and an image forming apparatus that can improve the performance of the pressure reducing mechanism and the ease of separating the recording medium. [Means for solving the problem]

[0008] In order to solve the above problems and achieve the object of the present invention, the secondary transfer device of the present invention includes a secondary transfer roller, a pressure-contacting mechanism, a pressure-reducing mechanism, and a support member. The secondary transfer roller contacts the intermediate transfer belt and, together with the opposing roller around which the intermediate transfer belt is wrapped, presses the intermediate transfer belt to form a transfer nip. The pressure-contacting mechanism applies nip pressure between the secondary transfer roller and the opposing roller with the intermediate transfer belt sandwiched therebetween. The pressure-reducing mechanism temporarily reduces the nip pressure when at least one of the leading and trailing ends of the recording medium passes through the transfer nip. The support member supports the secondary transfer roller so that its position in the recording medium transport direction can be changed.

[0009] The image forming apparatus of the present invention includes the above-described secondary transfer device. [Effects of the Invention]

[0010] According to the secondary transfer device and image forming apparatus having the above configuration, it is possible to improve the performance of the pressure reducing mechanism and the ease of separating the recording medium. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating the overall configuration of an image forming apparatus according to an embodiment of the present invention; [Figure 2] 1 is a side view showing a secondary transfer device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view taken along the line AA shown in FIG. 2. [Figure 4] FIG. 3 is a cross-sectional view taken along the line BB shown in FIG. 2. [Figure 5] 1 is a perspective view showing an example of a roller position adjusting mechanism of a secondary transfer device according to an embodiment of the present invention. [Figure 6] 10A and 10B are diagrams illustrating a state in which the secondary transfer roller is moved in the roller position adjustment mechanism according to the embodiment. [Figure 7] 10A and 10B are diagrams illustrating a state in which the secondary transfer roller is moved in the roller position adjustment mechanism according to the embodiment. [Figure 8] 10 is a perspective view showing another example of the roller position adjusting mechanism of the secondary transfer device according to the embodiment of the present invention. FIG. [Figure 9] 10A and 10B are diagrams illustrating a state in which the secondary transfer roller is moved in another embodiment of the roller position adjustment mechanism. [Figure 10] 10 is a diagram showing the position of the secondary transfer roller when decompressing the secondary transfer device according to the embodiment of the present invention. FIG. [Figure 11] 11A and 11B are diagrams showing the positional relationship between the secondary transfer roller and the opposing roller when the pressure is reduced. [Figure 12] 10A and 10B are diagrams illustrating differences in the amount of pressure reduction depending on the position of the secondary transfer roller during pressure reduction. [Figure 13] 10 is a diagram showing the position of the secondary transfer roller when pressure reduction is not performed in the secondary transfer device according to the embodiment of the present invention. FIG. [Figure 14]14A and 14B are diagrams showing the ejection direction of the recording medium depending on the position of the secondary transfer roller. [Figure 15] 10 is a diagram showing the positional relationship between the secondary transfer roller and the opposing roller when pressure reduction is not performed in the secondary transfer device according to the embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to Figures 1 to 15. Note that common members in each figure are given the same reference numerals. Furthermore, the present invention is not limited to the following embodiments.

[0013] 1. Example of implementation 1-1.Configuration of image forming device First, the overall configuration of an image forming apparatus according to an embodiment of the present invention (hereinafter referred to as "this example") will be described. Fig. 1 is a schematic diagram of an image forming apparatus 10 according to this example.

[0014] The image forming device 10 shown in FIG. 1 forms an image on paper using an electrophotographic method, and is a tandem color image forming device that overlays four colors of toner: yellow (Y), magenta (M), cyan (C), and black (Bk).

[0015] The image forming device 10 includes a document reading unit 11 equipped with an automatic document feeder (ADF), an operation display unit 12, a control unit 13, a paper feed tray 14, a fixing device 15, a conveying unit 16, a paper output tray 17, and an image forming unit 20.

[0016] The document reading unit 11 optically reads an image from a document on the document feed tray of the ADF, performs A / D conversion on the read image, and generates image data (scan data).The document reading unit 11 then outputs the generated image data to the control unit 13.

[0017] The operation display unit 12 is configured as a touch panel in which a touch sensor as an operation input unit is superimposed on a display unit made of an LCD (Liquid Crystal Display), an organic EL (Electro Luminescence) display, or the like. Note that in this example, the display unit and the operation input unit are formed integrally, but this is not limiting. The operation input unit using buttons, keys, etc. and the display unit using an LCD, etc., may be configured separately.

[0018] The operation display unit 12 generates an operation signal representing the content of an operation input by the user to the operation unit, and supplies the operation signal to the control unit 13. For example, when an operation instructing the start of image formation processing is input by the user, the operation display unit 12 generates a signal to start the image formation processing and supplies the signal to the control unit 13. Furthermore, for example, the operation display unit 12 displays the content of the operation by the user, setting information, etc. on the display unit based on a display signal supplied from the control unit 13.

[0019] The paper feed tray 14 is a container that stores paper sheets on which images are formed in the image forming unit 20. The image forming apparatus 10 shown in FIG. 1 has two paper feed trays 14, but the number of paper feed trays 14 is not limited to this, and may be one, or three or more.

[0020] The transport unit 16 transports the paper fed from the paper feed tray 14 to the paper output tray 17. The transport unit 16 is provided with a plurality of rollers (transport rollers) for transporting the paper. Note that, although the configuration in which the transport unit 16 does not have a path or mechanism for double-sided printing is illustrated, the present invention is not limited to this, and the present invention may be applied to an image forming apparatus that has a path and mechanism for double-sided printing.

[0021] The image forming section 20 includes four image forming units 22Y, 22M, 22C, and 22K for forming toner images of the respective colors of Y, M, C, and K. Each of the image forming units 22Y, 22M, 22C, and 22K includes a charging section, an LED writing unit (laser light source) 26, a photosensitive drum 24, and a developing section.

[0022] The developing unit forms a latent image on the surface (outer periphery) of the photosensitive drum 24 and causes toner supplied from a developing device (not shown) to adhere to the latent image, thereby forming a toner image on the photosensitive drum 24.

[0023] In the following description, when it is not necessary to distinguish between the image forming units 22Y, 22M, 22C, and 22K, they will be collectively referred to as image forming units 22.

[0024] The image forming unit 20 also includes an intermediate transfer belt 21 and a secondary transfer device 30. The intermediate transfer belt 21 is formed in an endless shape and is wound around a plurality of pulleys. A cleaning device 27 is also provided on the intermediate transfer belt 21.

[0025] The intermediate transfer belt 21 is rotated by a drive motor (not shown) in a clockwise direction (the direction of arrow A in the figure), which is opposite to the rotation direction of the photosensitive drums 24. As the intermediate transfer belt 21 rotates, the toner images formed on the photosensitive drums 24 of the image forming units 22Y, 22M, 22C, and 22K of each color are sequentially transferred onto the intermediate transfer belt 21 and superimposed on each other. As a result, a full-color image is synthesized on the intermediate transfer belt 21.

[0026] The toner image formed on the intermediate transfer belt 21 is transferred (secondary transfer) from the intermediate transfer belt 21 onto a sheet of paper by a secondary transfer device 30 disposed at a secondary transfer position D. In addition, toner remaining on the intermediate transfer belt 21 after the secondary transfer is removed from the intermediate transfer belt 21 by a cleaning device 27 disposed downstream of the secondary transfer position D.

[0027] Fixing device 15 is provided downstream of secondary transfer position D of secondary transfer device 30 in the transport direction of transport section 16. Fixing device 15 applies pressure and heat to the paper to fix the toner image transferred onto the surface of the paper at secondary transfer position D. The paper on which the toner image has been fixed by fixing device 15 is transported on transport section 16 and discharged onto paper output tray 17.

[0028] The transport unit 16 is composed of transport rollers and guides that form the transport unit, as well as a motor that drives the transport rollers. Although not shown, the transport unit 16 is also equipped with a paper reversing mechanism for double-sided printing that turns over the paper that has left the fixing device 15 and sends it back to the transport unit upstream of the secondary transfer position D.

[0029] The control unit 13 is mainly composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The CPU executes processes in accordance with programs stored in the ROM, thereby realizing the various functions of the image forming apparatus 10. The control unit 13 controls the operations of the conveying unit 16, the image forming unit 20, the secondary transfer device 30, etc.

[0030] 1-2.2 Configuration of the transcription device Next, the state of the secondary transfer device 30 will be described with reference to Figures 2 to 4. Figure 2 is a side view showing the secondary transfer device 30, Figure 3 is a cross-sectional view taken along line AA in Figure 2, and Figure 4 is a cross-sectional view taken along line BB in Figure 2.

[0031] The secondary transfer device 30 presses a secondary transfer roller 41 of a secondary transfer unit 40 (described later) against the outer circumferential surface of the intermediate transfer belt 21 at a secondary transfer position D. The secondary transfer device 30 then sandwiches the intermediate transfer belt 21 between itself and a roller (opposing roller 28) that is positioned opposite the secondary transfer roller 41 among the multiple rollers around which the intermediate transfer belt 21 is wound, thereby forming a transfer nip. Hereinafter, the width direction of the intermediate transfer belt 21 will be referred to as the "front-rear direction." Furthermore, the relative position on the end side in the front-rear direction will be referred to as the "outside," and the relative position closer to the center in the front-rear direction will be referred to as the "inside."

[0032] 2 to 4, the secondary transfer device 30 has a secondary transfer unit 40, a pressure-bonding mechanism 50, a pressure-reducing mechanism 70, and a frame member 32 that supports these. The frame member 32 has a bottom surface portion 32a and a pair of support plates 32b. The bottom surface portion 32a is a substantially rectangular, flat-plate member that extends in the front-rear direction of the secondary transfer device 30. The support plates 32b are provided at both longitudinal ends of the bottom surface portion 32a.

[0033] The pair of support plates 32b face each other with the bottom surface portion 32a sandwiched therebetween. The lower portions of the support plates 32b are fixed to the bottom surface portion 32a with, for example, screws. The support plates 32b are formed so that their upper portions are narrower than their lower portions on the bottom surface portion 32a side. A unit support shaft 34 and a support shaft 36 are provided on the upper portions of the support plates 32b. The support shaft 36 is located lower on the support plates 32b than the unit support shaft 34.

[0034] The unit support shaft 34 and the support shaft 36 protrude outward in the front-rear direction from the upper part of the support plate 32b. The secondary transfer unit 40 is supported so as to be able to swing on the unit support shaft 34. Furthermore, the pressure-bonding mechanism 50 is supported so as to be able to swing on the support shaft 36.

[0035] Next, the secondary transfer unit 40 will be described. The secondary transfer unit 40 has a secondary transfer roller 41 and a support member 42 that rotatably supports the secondary transfer roller 41. The support member 42 rotatably supports the secondary transfer roller 41 so that the axial direction of the secondary transfer roller 41 is parallel to the width direction of the intermediate transfer belt 21. The support member 42 is also provided with a roller position adjustment mechanism that changes (adjusts) the position of the secondary transfer roller 41 along the paper transport direction. The configuration of the roller position adjustment mechanism will be described later.

[0036] The end of the support member 42 opposite to the end supporting the secondary transfer roller 41 is swingably supported by the unit support shaft 34. The secondary transfer roller 41 has a shaft portion 41a disposed at a predetermined distance downstream in the paper transport direction from the unit support shaft 34. The secondary transfer roller 41 and the support member 42 swing around the unit support shaft 34, causing the secondary transfer roller 41 to move between a pressing position and a release position.

[0037] Next, the crimping mechanism 50 will be described. The pressure mechanism 50 displaces the secondary transfer unit 40 so that it moves between a pressing position where the secondary transfer roller 41 presses against the intermediate transfer belt 21 to form a transfer nip and a spaced position where the secondary transfer roller 41 is separated from the intermediate transfer belt 21. The pressure mechanism 50 applies nip pressure between the secondary transfer roller 41 and the opposing roller 28 with the intermediate transfer belt 21 sandwiched therebetween. The pressure mechanism 50 has a first drive unit 52, a rotary shaft 53, a pressure cam 54, a pressure arm 55, and a biasing spring 56. The pressure cam 54 and the pressure arm 55 are provided at both ends in the front-rear direction corresponding to each support plate 32b.

[0038] The rotary shaft 53 is rotatably supported by the pair of support plates 32b. The axial direction of the rotary shaft 53 is arranged parallel to the axial direction of the secondary transfer roller 41. The rotary shaft 53 is rotationally driven by the first drive unit 52. Pressure cams 54 are provided on both ends of the rotary shaft 53 in the axial direction. The pressure cams 54 rotate together with the rotary shaft 53. An abutment roller 55b of a pressure arm 55 abuts against the pressure cam 54.

[0039] The pressure-contacting arm 55 is swingably supported by a support shaft 36 attached to the support plate 32b. The pressure-contacting arm 55 has a rotation fulcrum 55a, which serves as the center of swing, a contact roller 55b, and an action arm 55c. The rotation fulcrum 55a is provided at one end of the pressure-contacting arm 55. The rotation fulcrum 55a is disposed in a position shifted downstream in the conveying direction from above the rotation shaft 53. The contact roller 55b is provided at the other end of the pressure-contacting arm 55. The contact roller 55b comes into contact with the pressure-contacting cam 54 and serves as a force point for the pressure-contacting arm 55.

[0040] The acting arm 55c protrudes upstream in the paper transport direction from the middle of the pressure arm 55. A biasing spring 56 is attached to the upper surface of the acting arm 55c near its tip. The upper end of the biasing spring 56 is joined to the underside of the tip of a pressure reducing arm 75, which will be described later. The point where the biasing spring 56 is attached near the tip of the acting arm 55c serves as the point of action of the pressure arm 55. When forming a transfer nip, the acting arm 55c of the pressure arm 55 presses the back surface of the secondary transfer unit 40 toward the opposing roller 28 via the biasing spring 56 and the pressure reducing arm 75.

[0041] The two pressure cams 54 arranged at both ends of the axial direction of the secondary transfer roller 41 are arranged in the same phase. When the pressure cam 54 and the contact roller 55b come into contact with each other, the two pressure arms 55 at both ends simultaneously press the rear surface of the secondary transfer unit 40 in the same manner at both ends of the axial direction, and then release the pressure.

[0042] Furthermore, the pressure mechanism 50 not only controls the pressing and releasing of the secondary transfer unit 40, but also changes the force of the pressure arm 55 pressing the secondary transfer unit 40 according to the rotation angle position of the pressure cam 54. This makes it possible to adjust the pressure with which the secondary transfer roller 41 presses the intermediate transfer belt 21. As a result, the nip pressure with which the secondary transfer roller 41 presses the intermediate transfer belt 21 between itself and the opposing roller 28 changes.

[0043] Next, the pressure reducing mechanism 70 will be described. The pressure reducing mechanism 70 temporarily reduces the nip pressure applied by the secondary transfer roller 41, which is in the pressing position, to pinch and press the intermediate transfer belt 21 between itself and the opposing roller 28, when at least one of the leading and trailing edges of the paper passes through the secondary transfer location D (between the secondary transfer roller 41 and the intermediate transfer belt 21). The pressure reducing mechanism 70 has a second drive unit 72, a pressure reducing rotation shaft 73, a pressure reducing cam 74, a pressure reducing arm 75, and a position detection sensor 76. The pressure reducing cam 74 and the pressure reducing arm 75 are provided at both ends in the front-rear direction, similar to the pressure contact cam 54 and the pressure contact arm 55.

[0044] The pressure reducing rotary shaft 73 is formed in a hollow cylindrical shape. The rotary shaft 53 of the crimping mechanism 50 passes through the cylindrical hole of the pressure reducing rotary shaft 73. That is, the pressure reducing rotary shaft 73 is fitted onto the rotary shaft 53 and is arranged coaxially with the rotary shaft 53. A pressure reducing cam 74 is attached to the pressure reducing rotary shaft 73.

[0045] The pressure-reducing cam 74 has an inclined portion and a flat portion on its outer periphery as regions where a reduced pressure state is created with a weakened nip pressure. In controlling the pressure-reducing mechanism 70, different regions of the pressure-reducing cam 74 are used depending on the length of time the reduced pressure is maintained. The pressure-reducing cam 74 is attached to the pressure-reducing rotation shaft 73, which is fitted onto the rotation shaft 53, and is thereby arranged coaxially with the pressure-reducing cam 54. The pressure-reducing cam 74 and the pressure-reducing cam 54 are positioned such that their projected images, projected in the axial direction of the secondary transfer roller 41, overlap to the maximum extent possible. The maximum diameter of the pressure-reducing cam 54 is set smaller than the minimum diameter of the pressure-reducing cam 74.

[0046] Furthermore, the decompression cams 74 are respectively disposed near the inside of the two pressure contact cams 54 disposed separately at both ends in the front-rear direction. Position detection sensors 76 are disposed inside the two decompression cams 74. The position detection sensors 76 detect the angular positions of the second drive unit 72 and the decompression cam 74. Information detected by the position detection sensors 76 is output to the control unit 13.

[0047] A rotor 78 provided on a decompression arm 75 abuts against the decompression cam 74. The decompression arm 75 is provided corresponding to the two pressure arms 55 at both ends in the front-rear direction. The decompression arm 75 is swingably supported on the support shaft 36. The decompression arm 75 has a pressing portion 75a. The pressing portion 75a is provided at one end of the decompression arm 75. The pressing portion 75a is disposed opposite to the rear surface of the secondary transfer unit 40. The pressing portion 75a presses the secondary transfer unit 40 toward the intermediate transfer belt 21. In addition, the upper end of the urging spring 56 abuts against the surface of the pressing portion 75a opposite to the surface facing the secondary transfer unit 40. The point of abutment with the urging spring 56 is a point of action 75b of the decompression arm 75 during the decompression operation.

[0048] The other end of the decompression arm 75 opposite the pressing portion 75a serves as a force point 75d that receives a force from the decompression cam 74. A connecting shaft 77 is connected to the other end of the decompression arm 75 that serves as the force point 75d. The connecting shaft 77 extends in the front-rear direction and connects the force points 75d of the two decompression arms 75 provided at both ends in the front-rear direction. A cylindrical rotating body 78 is attached to this connecting shaft 77. The rotating body 78 rotates around the center of the connecting shaft 77.

[0049] The decompression arm 75 swings around the rotation fulcrum 75c as the rotor 78 comes into contact with the decompression cam 74. By using the rotor 78 as the member that comes into contact with the decompression cam 74, it is possible to reduce friction with the decompression cam 74 and improve the durability of the decompression cam 74. Note that the connecting shaft 77 may come into direct contact with the decompression cam 74 without providing the rotor 78.

[0050] Here, a rotation fulcrum 75c, which is the swing center of the decompression arm 75, is located at a position slightly closer to the force point 75d than the center of the decompression arm 75 in the longitudinal direction. The rotation fulcrum 75c is rotatably supported on the support shaft 36 of the support plate 32b so as to be coaxial with the rotation fulcrum 55a of the crimping arm 55. Here, the decompression arm 75 is set so that the distance from the rotation fulcrum 75c to the point of action 75b during the decompression operation is longer than the distance from the force point 75d, at which the force from the decompression cam 74 is received, to the rotation fulcrum 75c. This makes it possible to reduce the driving force that swings the decompression arm 75, thereby enabling the second drive unit 72 to be made smaller and more cost-effective.

[0051] The pressure reducing mechanism 70 is configured such that the force point 75d of the pressure reducing arm 75, i.e., the point that abuts against the pressure reducing cam 74, is located between the rotation fulcrum 55a of the pressure reducing arm 55 and the pressure reducing cam 54. This results in a configuration in which the main part of the pressure reducing mechanism 70 is contained within the pressure reducing mechanism 50, thereby enabling the overall size of the secondary transfer device 30 to be reduced.

[0052] 1-3. Roller position adjustment mechanism Next, the configuration of a roller position adjustment mechanism that adjusts the position of the secondary transfer roller 41 will be described with reference to Figs. 5 to 9. Fig. 5 is a perspective view showing one embodiment of the roller position adjustment mechanism. Figs. 6 and 7 are views showing a state in which the secondary transfer roller in one embodiment of the roller position adjustment mechanism has been moved.

[0053] 5, the support member 42 is provided with a support hole 42a through which the shaft portion 41a of the secondary transfer roller 41 passes. As one example of a roller position adjustment mechanism, an eccentric cam 45 is rotatably fitted into the support hole 42a. The eccentric cam 45 also serves as a bearing portion that rotatably supports the shaft portion 41a of the secondary transfer roller 41. The shaft portion 41a of the secondary transfer roller 41 is provided at a position eccentric from the axis of the eccentric cam 45.

[0054] 6 and 7, by rotating the eccentric cam 45, the shaft 41a of the secondary transfer roller 41 moves along the paper transport direction. This allows the secondary transfer roller 41 to approach or move away from the unit support shaft 34 or the support shaft 36, and the position of the secondary transfer roller 41 can be changed (adjusted) to a desired position. The rotation of the eccentric cam 45 may be performed by a motor or may be rotated manually.

[0055] 8 and 9 are diagrams showing other embodiments of the roller position adjusting mechanism. 8 and 9, the support hole 42a of the support member 42 according to another embodiment is formed as an elongated hole. The support hole 42a is formed so that its length in the paper transport direction is longer than in other directions. A slide plate 46 is attached to the support member 42 at the location where the support hole 42a is formed. The slide plate 46, which represents another embodiment of the roller position adjustment mechanism, is supported on the support member 42 so as to be movable along the paper transport direction.

[0056] The slide plate 46 rotatably supports the shaft 41a of the secondary transfer roller 41. By moving the slide plate 46, the shaft 41a of the secondary transfer roller 41 moves along the paper transport direction. This allows the secondary transfer roller 41 to approach or move away from the unit support shaft 34 or the support shaft 36, and the position of the secondary transfer roller 41 can be changed (adjusted) to a desired position. The slide plate 46 may be moved by a motor using a cam mechanism or a belt mechanism, or it may be moved manually.

[0057] Furthermore, the roller position adjustment mechanism changes (adjusts) the secondary transfer roller 41 to at least two positions: a position close to the support shaft 36 and a position away from the support shaft 36. The position of the secondary transfer roller 41 may be configured to be changeable (adjustable) to three or more positions.

[0058] 3. Example of secondary transfer device operation Next, an example of the operation of the secondary transfer device 30 having the above-described configuration will be described with reference to FIGS.

[0059] 3-1. Decompression operation First, an example of operation when decompressing will be described with reference to FIGS. FIG. 10 is a diagram showing the position of the secondary transfer roller when decompression is performed.

[0060] First, in the secondary transfer device 30, when the first drive unit 52 rotates the rotary shaft 53 of the pressure mechanism 50, the pressure cam 54 attached to the rotary shaft 53 rotates. Then, the pressure arm 55, whose contact roller 55b abuts against the pressure cam 54, swings around the rotation fulcrum 55a in accordance with the angular position of the pressure cam 54. This adjusts the nip pressure between the secondary transfer roller 41 and the opposing roller 28.

[0061] When the pressure reduction mechanism 70 is not applying pressure, the pressure reduction cam 74 is at an angular position where it does not contact the force point 75d of the pressure reduction arm 75, i.e., the rotor 78 of the connecting shaft 77. In this state, the pressure reduction arm 75 does not receive force from the pressure reduction cam 74, and is displaced in accordance with the crimping operation of the crimping mechanism 50.

[0062] Then, when the pressure reducing cam 74 of the pressure reducing mechanism 70 is rotated to a predetermined angle position while the pressure reducing cam 54 of the pressure reducing mechanism 50 is held, the pressure reducing cam 74 comes into contact with the force point 75d of the pressure reducing arm 75, i.e., the rotor 78 of the connecting shaft 77. As a result, the pressure reducing arm 75 rotates around the rotation fulcrum 75c, and is displaced to a position where the pressure applying point 75b, which is at the end opposite the force point 75d across the rotation fulcrum 75c, pushes back the pressure reducing arm 55 via the biasing spring 56.

[0063] The pressure reducing arm 75 reduces the nip pressure by blocking the pressing force exerted by the pressure arm 55 on the secondary transfer unit 40 via the biasing spring 56. At this time, the axial distance between the opposing roller 28 and the secondary transfer roller 41 becomes somewhat shorter than the sum of the radii of the opposing roller 28 and the secondary transfer roller 41 when not in contact. Therefore, the nip pressure is generated by the elasticity of the outer peripheral members of the secondary transfer roller 41 and the opposing roller 28. This allows the pressure reducing mechanism 70 to easily and smoothly create a temporary reduced pressure state at the appropriate timing.

[0064] Before performing the above-described decompression operation, the roller position adjustment mechanism is used to move the secondary transfer roller 41 downstream in the conveyance direction, that is, in a direction away from the rotation fulcrum 75c of the decompression arm 75, as shown in FIG.

[0065] 11A and 11B are diagrams showing the positional relationship between the secondary transfer roller and the opposing roller when the pressure is reduced. 11A shows a case where the secondary transfer roller 41 is located upstream in the conveyance direction of the opposing roller 28 relative to a normal M1 to the intermediate transfer belt 21. In this case, as shown in FIG. 11A, the secondary transfer roller 41 is disposed on a tension portion 21a of the intermediate transfer belt 21 that is tensioned by a plurality of rollers 28. Therefore, a portion Q1 of the tension portion 21a of the intermediate transfer belt 21 that comes into contact with the secondary transfer roller 41 is pressed by the secondary transfer roller 41.

[0066] In this state, when the pressure applied to the secondary transfer roller 41 is reduced by the pressure reducing mechanism 70, the pressure applied by the secondary transfer roller 41 at the position Q1 of the intermediate transfer belt 21 is also reduced. As a result, the tension of the intermediate transfer belt 21 changes, causing fluctuations in the rotation speed of the intermediate transfer belt 21.

[0067] In contrast, in the secondary transfer device 30 of this example, as shown in FIG. 11B, the secondary transfer roller 41 is moved downstream in the conveyance direction from the normal M1 of the opposing roller 28. As a result, the secondary transfer roller 41 is disposed at a position that is away from the tension portion 21a of the intermediate transfer belt 21 and the position Q1 in FIG. 11A. Therefore, no pressing force from the secondary transfer roller 41 acts on the tension portion 21a of the intermediate transfer belt 21. Therefore, even if the pressure reducing mechanism 70 reduces the pressing force on the secondary transfer roller 41, the tension of the intermediate transfer belt 21 is not affected. As a result, it is possible to prevent speed fluctuations in the intermediate transfer belt 21, and it is possible to improve the performance of the pressure reducing mechanism 70.

[0068] FIG. 12 is a diagram showing the difference in the amount of pressure reduction depending on the position of the secondary transfer roller 41 during pressure reduction. 12, by moving the secondary transfer roller 41 downstream in the transport direction, the secondary transfer roller 41 can be moved away from the rotation fulcrum 75c of the pressure-reducing arm 75 of the pressure-reducing mechanism 70. That is, the position of the action point 75b of the pressure-reducing arm 75 that presses the secondary transfer roller 41 can also be moved away from the rotation fulcrum 75c. Furthermore, since the distance from the rotation fulcrum 75c to the action point 75b can be increased, the torque and time required for the pressure-reducing operation can be reduced, thereby improving the performance of the pressure-reducing mechanism 70.

[0069] In this way, the amount of pressure reduction by the pressure reduction mechanism 70 can be increased, so that it is possible to handle paper that has a large basis weight or is thick, and that experiences a large impact on the transfer nip.

[0070] 3-2. When decompression is not performed Next, a case where pressure reduction is not performed will be described with reference to FIGS. FIG. 13 is a diagram showing the position of the secondary transfer roller when no pressure reduction is performed.

[0071] When pressure reduction is not performed, the roller position adjustment mechanism is used to move the secondary transfer roller 41 upstream in the conveyance direction, that is, in a direction approaching the rotation fulcrum 75c of the pressure reduction arm 75, as shown in Fig. 13. Because pressure reduction is not performed, even if the secondary transfer roller 41 is placed on the tension portion 21a of the intermediate transfer belt 21 as shown in Fig. 11A, the tension of the intermediate transfer belt 21 does not change. Therefore, no speed fluctuation occurs in the intermediate transfer belt 21.

[0072] 14A and 14B are diagrams showing the discharge direction of the paper P1 depending on the position of the secondary transfer roller 41. FIG. As shown in FIG. 14A, when the secondary transfer roller 41 is located downstream in the transport direction of the paper P1, the discharge direction of the paper P1 faces upward in the vertical direction along the intermediate transfer belt 21. As a result, there is a risk that the paper P1 will not be separated from the intermediate transfer belt 21. In contrast, as shown in FIG. 14B, when the secondary transfer roller 41 is located upstream in the transport direction of the paper P1, the discharge direction of the paper P1 faces downward in the vertical direction. This improves the separation of the paper P1 from the intermediate transfer belt 21 after it has passed through the transfer nip.

[0073] FIG. 15 is a diagram showing the positional relationship between the secondary transfer roller 41 and the opposing roller 28 when no pressure reduction is performed. 15, a conveyance guide plate 61 that conveys paper to the fixing device 15 is provided between the secondary transfer device 30 and the fixing device 15. When pressure reduction is not performed, a line M2 (hereinafter referred to as a middle line) that is perpendicular to the line connecting the axis of the secondary transfer roller 41 and the axis of the opposing roller 28 is inclined with respect to a line P3 (hereinafter referred to as a parallel line) that is parallel to the conveyance guide plate 61. More specifically, the downstream side of the middle line M2 in the conveyance direction is inclined so as to face downward in the up-down direction with respect to the parallel line P3. This allows paper that has passed through the transfer nip to be discharged toward the conveyance guide plate 61, improving the separation and conveyance of paper.

[0074] In this way, according to the secondary transfer device 30 of this example, by changing the position of the secondary transfer roller 41 depending on the implementation of pressure reduction, it is possible to simultaneously achieve improved performance of the pressure reduction mechanism and improved paper separation performance.

[0075] Furthermore, as described above, the position of the secondary transfer roller 41 is not limited to two positions, a position close to the support shaft 36 and a position away from the support shaft 36, but may be configured to be adjustable to three or more positions. The position of the secondary transfer roller 41 may be changed (adjusted) depending on the type of paper that is the recording medium. For example, in the case of paper with a large basis weight or a thick paper, the pressure is reduced and the secondary transfer roller 41 is moved to a position further away from the support shaft 36. This allows the amount of pressure reduction by the pressure reduction mechanism 70 to be increased and prevents speed fluctuations in the intermediate transfer belt 21.

[0076] Furthermore, in the case of paper with a small basis weight, thin paper thickness, or coated paper, the pressure is not reduced and the secondary transfer roller 41 is moved to a position closer to the support shaft 36. This further improves the separation of the paper from the intermediate transfer belt 21.

[0077] Coated paper has poorer separability from the intermediate transfer belt 21 than uncoated paper. Therefore, for papers of the same basis weight or thickness, it is preferable to move the secondary transfer roller 41 closer to the support shaft 36 for coated paper than for uncoated paper.

[0078] Furthermore, the control unit 13 may adjust the rotation angle of the pressure cam 54 of the pressure mechanism 50 depending on the type of paper, and adjust the nip pressure created by the secondary transfer roller 41 and the opposing roller 28. For example, in the case of paper with a small basis weight, thin paper thickness, or coated paper, the control unit 13 controls the pressure mechanism 50 to increase the nip pressure.

[0079] The setting conditions, such as the position of the secondary transfer roller 41, whether or not to reduce pressure, and the magnitude of the nip pressure by the pressing mechanism 50, are stored in advance in a memory unit of the control unit 13 according to the type of paper. When the paper on which an image is to be formed is set, the control unit 13 outputs the setting conditions, which are selected from the multiple setting conditions stored in the memory unit according to the type of paper, to the operation display unit 12 and the secondary transfer device 30. Then, the pressing mechanism 50 and the pressure reducing mechanism 70 drive the first drive unit 52 and the second drive unit 72 based on the setting conditions output from the control unit 13.

[0080] The roller position adjustment mechanism may also be provided with a drive unit that exerts a drive force to change the position of the secondary transfer roller 41. The roller position adjustment mechanism then drives the drive unit based on setting conditions output from the control unit 13. Note that the position of the secondary transfer roller 41 may be changed (adjusted) by manually operating the roller position adjustment mechanism based on information displayed on the operation display unit 12.

[0081] The above describes the embodiments, including their effects. However, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the invention as defined in the claims.

[0082] In the above-described embodiment, a color image is formed using four sets of image forming units, but the image forming apparatus according to the present invention may also be configured to form a monochrome image using one image forming unit.

[0083] Furthermore, some or all of the above-described components, functions, processing units, etc. may be implemented in hardware, for example, by designing an integrated circuit. Furthermore, the above-described components, functions, etc. may be implemented in software by a processor interpreting and executing a program that implements each function. Information such as the programs, tables, and files that implement each function can be stored in a storage device such as a memory, a hard disk, or an SSD (Solid State Drive), or in a storage medium such as an IC card, SD card, or DVD.

[0084] Furthermore, although an example in which paper is used as the recording medium has been described, the present invention is not limited to this, and various other materials such as film and fabric can also be used as the recording medium.

[0085] In this specification, the words "parallel" and "orthogonal" are used, but these do not mean only "parallel" and "orthogonal" in the strict sense, but also include "parallel" and "orthogonal" and may also mean a "substantially parallel" or "substantially orthogonal" state within a range in which the functions can be exerted. [Explanation of symbols]

[0086] 10...image forming device, 11...document reading section, 12...operation display section, 13...control section, 14...paper feed tray, 15...fixing device, 16...conveying section, 17...paper output tray, 20...image forming section, 21...intermediate transfer belt, 21a...tensioning section, 22...image forming unit, 28...opposing roller, 30...secondary transfer device, 32...frame member, 32a...bottom section, 32b...support plate, 34...unit support shaft, 36...support shaft, 40...secondary transfer unit, 41...secondary transfer roller, 41a...shaft section, 42...support member, 42a...support hole, 45...eccentric cam, 46...slide plate, 50...pressing mechanism, 52...first drive section, 53...rotating shaft, 54...pressing cam, 55...pressing arm, 55a...rotation fulcrum, 55b...contact roller, 55c...action arm, 61...transport guide plate, 70...pressure reduction mechanism, 72...second drive unit, 73...pressure reduction rotation shaft, 74...pressure reduction cam, 75...pressure reduction arm, 75a...pressure unit, 75b...action point, 75c...rotation fulcrum, 75d...force point, 76...position detection sensor, 77...connecting shaft, 78...rotating body, M1...normal line, M2...intermediate line, P1...paper (recording medium), P3...parallel line

Claims

1. a secondary transfer roller that contacts the intermediate transfer belt and presses the intermediate transfer belt together with an opposing roller around which the intermediate transfer belt is wound, thereby forming a transfer nip; a pressing mechanism that applies nip pressure between the secondary transfer roller and the opposing roller with the intermediate transfer belt sandwiched therebetween; a pressure reducing mechanism that temporarily reduces the nip pressure when at least one of the leading and trailing ends of the recording medium passes through the transfer nip; a support member that supports the secondary transfer roller so that the position of the secondary transfer roller in the conveyance direction of the recording medium can be changed; Equipped with The position of the secondary transfer roller is changed depending on whether or not the pressure is reduced by the pressure reducing mechanism. Secondary transfer device.

2. When the pressure is reduced by the pressure reducing mechanism, the secondary transfer roller is located downstream in the recording medium conveyance direction from a normal to the intermediate transfer belt at an upstream end in the recording medium conveyance direction of the surface where the counter roller and the intermediate transfer belt contact each other. The secondary transfer device according to claim 1 .

3. When the pressure is not reduced by the pressure reducing mechanism, the secondary transfer roller is located upstream in the recording medium conveyance direction from a normal to the intermediate transfer belt at an upstream end in the recording medium conveyance direction of the surface where the counter roller and the intermediate transfer belt contact each other. The secondary transfer device according to claim 1 or 2.

4. When the pressure reduction mechanism is not performed, the secondary transfer roller is positioned such that a line perpendicular to a line connecting the axis of the counter roller and the axis of the secondary transfer roller is inclined with respect to a line parallel to a transport guide plate disposed downstream of the secondary transfer roller in the transport direction. The secondary transfer device according to claim 3 .

5. the pressure reducing mechanism includes a pressure reducing arm that is swingably supported by the support member and presses the secondary transfer roller; a rotation fulcrum that is the swing center of the pressure reducing arm is located upstream of the secondary transfer roller in the recording medium conveyance direction; The secondary transfer roller is positioned in a direction approaching or moving away from a rotation fulcrum that is the swing center of the pressure reduction arm, depending on whether or not the pressure reduction mechanism is performing pressure reduction. The secondary transfer device according to claim 1 .

6. When the pressure is reduced by the pressure reducing mechanism, the secondary transfer roller is moved in a direction away from the rotation fulcrum of the pressure reducing arm. The secondary transfer device according to claim 5 .

7. When the pressure reduction mechanism does not reduce the pressure, the secondary transfer roller is moved in a direction approaching the rotation fulcrum of the pressure reduction arm.

7. The secondary transfer device according to claim 5 or 6.

8. The position of the secondary transfer roller is changed depending on the type of the recording medium. The secondary transfer device according to claim 1 .

9. The secondary transfer roller is positioned at a position farther away from the rotation fulcrum of the pressure reducing arm as the basis weight or thickness of the recording medium increases. The secondary transfer device according to claim 5 .

10. The smaller the basis weight or thickness of the recording medium, the closer the secondary transfer roller is to the rotation fulcrum of the pressure reducing arm. The secondary transfer device according to claim 5 .

11. The smaller the basis weight or thickness of the recording medium, the stronger the nip pressure applied by the pressing mechanism. The secondary transfer device according to claim 10 .

12. The position of the secondary transfer roller is changed depending on whether the recording medium is coated paper or not. When the recording medium is coated paper, the recording medium is positioned close to the rotation fulcrum of the pressure reducing arm. The secondary transfer device according to claim 5 .

13. A control unit that controls driving of the pressure bonding mechanism and driving of the pressure reducing mechanism is further provided. The control unit controls the strength of the nip pressure by the pressure bonding mechanism and whether or not the pressure reduction mechanism reduces pressure depending on the type of the recording medium. The secondary transfer device according to claim 8 .

14. the control unit stores a plurality of setting conditions for setting the position of the secondary transfer roller, the strength of the nip pressure by the pressing mechanism, and whether or not the pressure reduction mechanism is to reduce the pressure, depending on the type of the recording medium; The control unit outputs a setting condition according to the type of the recording medium from the plurality of setting conditions stored. The secondary transfer device according to claim 13 .

15. An eccentric cam for changing the position of the secondary transfer roller is rotatably attached to the support member. The secondary transfer device according to claim 1 .

16. a slide plate supported on the support member so as to be movable along a transport direction of the recording medium; The secondary transfer roller is rotatably supported by the slide plate. The secondary transfer device according to claim 1 .

17. an intermediate transfer belt around which a plurality of rollers are wound; a secondary transfer device that transfers the toner image formed on the intermediate transfer belt onto a recording medium, The secondary transfer device a secondary transfer roller that contacts the intermediate transfer belt and presses the intermediate transfer belt together with a counter roller around which the intermediate transfer belt is wound, forming a transfer nip; a pressing mechanism that applies nip pressure between the secondary transfer roller and the opposing roller with the intermediate transfer belt sandwiched therebetween; a pressure reducing mechanism that temporarily reduces the nip pressure when at least one of the leading and trailing ends of the recording medium passes through the transfer nip; a support member that supports the secondary transfer roller so that the position of the secondary transfer roller in the conveyance direction of the recording medium can be changed; Equipped with The position of the secondary transfer roller is changed depending on whether or not the pressure is reduced by the pressure reducing mechanism. Image forming device.

Images