Transfer unit and image forming device having the same

Abstract

The present invention provides a transfer unit and an image forming device having the transfer unit. The transfer unit of the present invention includes a first roller as a transfer roller, a second roller whose elastic layer has an axial length greater than that of the first roller, a first bearing component, a second bearing component, a roller bracket, a first force-applying component, a second force-applying component, a switching cam, a driving mechanism, and a first transfer front guide. By rotating the roller bracket, the first roller or the second roller is arranged opposite to the image carrier, and by rotating the switching cam, the first roller or the second roller arranged opposite to the image carrier is selectively arranged at a reference position where it is pressed against the image carrier and a separation position where it is separated from the image carrier. When the first roller or the second roller is arranged at the reference position, the first transfer front guide is arranged at the first guide position.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus including a transfer unit for transferring a toner image formed on an image carrier such as a photosensitive drum or an intermediate transfer belt to a recording medium and the transfer unit. Background Art

[0002] In the past, there is a known image forming device with an intermediate transfer method, which includes an endless intermediate transfer belt rotating in a specified direction and a plurality of image forming units arranged along the intermediate transfer belt. After the colorant images of each color are sequentially overlapped on the intermediate transfer belt for primary transfer by each image forming unit, the colorant images are secondarily transferred to a recording medium such as paper by a secondary transfer roller.

[0003] In such an image forming apparatus using the intermediate transfer method, the toner adheres to the surface of the secondary transfer roller due to the long-term printing. In particular, in order to improve the colorability and color reproducibility, it is necessary to perform calibration to correct the image density and color misregistration at a predetermined time. However, when the calibration is performed, the patch image formed on the intermediate transfer belt is not transferred to the paper but is removed by the belt cleaning device. Therefore, when the patch image passes through the secondary transfer roller, part of the toner transferred to the intermediate transfer belt adheres to the secondary transfer roller.

[0004] Conventionally, a method of cleaning the secondary transfer roller is used in which a transfer reverse voltage (voltage with the same polarity as the toner) is applied to the secondary transfer roller when no image is formed, so that the toner attached to the secondary transfer roller is returned to the intermediate transfer belt. However, this method takes time to clean the secondary transfer roller, so there is a problem that the printing waiting time becomes longer.

[0005] Therefore, a method for improving productivity by being able to switch the secondary transfer roller to a size suitable for the recording medium has been proposed. For example, the following image forming device is known, comprising: a rotating body having a plurality of secondary transfer rollers with axial lengths different from each other, and a holding portion supporting the plurality of secondary transfer rollers so as to be rotatable and rotatable around an axis parallel to the axial direction; and a control portion that selects one roller from the plurality of secondary transfer rollers according to the width of the recording medium and rotates the holding portion so that one roller is opposed to the intermediate transfer belt. Summary of the invention

[0006] An object of the present invention is to provide a transfer unit and an image forming apparatus having the transfer unit, which can realize switching of two transfer rollers selectively pressed against an image carrier with a simple structure and can also maintain the positional relationship with a pre-transfer guide.

[0007] The transfer unit of the first structure of the present invention includes a transfer roller, the transfer roller having a core shaft and an elastic layer stacked on the outer peripheral surface of the core shaft, the elastic layer is pressed against the image carrier to form a transfer roller gap, and the transfer unit transfers the toner image formed on the image carrier to the recording medium passing through the transfer roller gap.

[0008] The transfer unit comprises:

[0009] a first roller as the transfer roller and a second roller having a greater axial length than the first roller for the elastic layer;

[0010] a first bearing member rotatably supporting the first roller;

[0011] a second bearing member rotatably supporting the second roller;

[0012] A roller bracket having a first bearing holding portion and a second bearing holding portion, wherein the first bearing holding portion and the second bearing holding portion respectively hold the first bearing component and the second bearing component so as to be able to slide in a direction approaching or separating from the image carrier;

[0013] A first force applying member is disposed between the first bearing holding portion and the first bearing member, and applies force to the first bearing member in a direction approaching the image carrier;

[0014] A second force applying member is disposed between the second bearing holding portion and the second bearing member, and applies force to the second bearing member in a direction approaching the image carrier;

[0015] A switching cam having a guide hole for engaging with a first engaging portion formed on the first bearing component and a second engaging portion formed on the second bearing component;

[0016] a driving mechanism for rotationally driving the roller bracket and the switching cam; and

[0017] The first pre-transfer guide is swingably supported by the unit frame on the upstream side of the transfer roller nip portion with respect to the conveying direction of the recording medium.

[0018] By rotating the roller holder, one of the first roller and the second roller is arranged to face the image carrier, and

[0019] By rotating the switching cam, the engagement positions of the first engagement portion and the second engagement portion in the guide hole are changed, and the first roller or the second roller arranged opposite to the image carrier is selectively arranged at a reference position where the first roller or the second roller is pressed against the image carrier to form a transfer roller gap and a separation position where the first roller or the second roller is separated from the image carrier.

[0020] When the first roller or the second roller is arranged at the reference position, the first pre-transfer guide is arranged at a first guide position capable of guiding the recording medium to the transfer roller nip portion by the rotation of the switching cam.

[0021] According to the first structure of the present invention, when the first roller or the second roller is arranged at the reference position, the first transfer front guide is arranged at the first guide position capable of guiding the recording medium to the transfer roller gap by the rotation of the switching cam. Thus, the positional relationship of the first transfer front guide relative to the transfer roller gap can be maintained when the first roller and the second roller are switched, and the recording medium can be smoothly guided to the transfer roller gap.

[0022] In addition, according to the second structure of the present invention, by switching the first roller or the second roller configured at the reference position according to the width dimension of the image data and the width dimension of the recording medium, an appropriate transfer roller corresponding to the image width and the width of the recording medium can be used, and the occurrence of poor transfer and contamination of the back side of the recording medium caused by the adhesion of colorant to the transfer roller can be effectively suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 1 is a diagram showing the internal structure of an image forming apparatus 100 including the secondary transfer unit 9 of the present invention.

[0024] Figure 2 yes Figure 1 An enlarged view of the vicinity of the image forming portion Pa in FIG.

[0025] Figure 3 It is a side cross-sectional view of the intermediate transfer unit 30 mounted in the image forming apparatus 100 .

[0026] Figure 4 It is a perspective view of the secondary transfer unit 9 according to one embodiment of the present invention mounted in the image forming apparatus 100 .

[0027] Figure 5 It is an enlarged perspective view showing the structure of one end side of the secondary transfer unit 9 according to the present embodiment.

[0028] Figure 6 This is a perspective view of the periphery of the roller holder 47 of the secondary transfer unit 9 according to the present embodiment as viewed from the rear side.

[0029] Figure 7 It is a perspective view showing a driving mechanism of the secondary transfer unit 9 according to the present embodiment.

[0030] Figure 8 This is a block diagram showing an example of a control route of the image forming apparatus 100 equipped with the secondary transfer unit 9 according to the present embodiment.

[0031] Fig. 9 1 is a side cross-sectional view including the switching cam 50 of the secondary transfer unit 9 according to the present embodiment, and is a view showing a state where the first roller 40 is arranged at a reference position for forming the secondary transfer nip portion N. FIG.

[0032] Fig.10 It is a top view of the switching cam 50 .

[0033] Fig.11 This means that the switching cam 50 is Fig. 9 FIG. 6 is a diagram showing a state in which the first pre-transfer guide 65 and the second pre-transfer guide 67 are moved by rotating the guide 65 in the clockwise direction by a predetermined angle.

[0034] Fig.12 This means that the switching cam 50 is Fig.11 FIG. 4 is a diagram of a first separated state of the first roller 40 in which the first roller 40 is rotated clockwise by a predetermined angle in the state of FIG.

[0035] Fig.13 This means that the switching cam 50 is Fig.12 FIG. 4 is a diagram of a second separated state of the first roller 40 in which the state of FIG. 4 is further rotated clockwise by a predetermined angle.

[0036] Fig.14 This means that the shaft 51 is Fig.13 FIG. 4 is a diagram of a state in which the second roller 41 and the driving roller 10 are opposed to each other in the counterclockwise direction.

[0037] Fig.15 This means that the switching cam 50 is Fig.14 FIG. 4 is a diagram of a state in which the second roller 41 is rotated counterclockwise by a predetermined angle and arranged at a reference position for forming the secondary transfer roller nip portion N.

[0038] Fig.16 This means that the switching cam 50 is Fig.15 FIG. 6 is a diagram showing a state in which the first pre-transfer guide 65 and the second pre-transfer guide 67 are moved by rotating the guide 65 in the clockwise direction by a predetermined angle.

[0039] Fig.17 This means that the switching cam 50 is Fig.16 FIG. 4 is a diagram of a first separated state of the second roller 41 in which the second roller 41 is rotated counterclockwise by a predetermined angle in the state of FIG.

[0040] Fig.18 This means that the switching cam 50 is Fig.17 FIG. 4 is a diagram of a second separated state of the second roller 41 in which the state is further rotated counterclockwise by a predetermined angle.

[0041] Fig.19 This means that the switching cam 50 is Fig.18FIG. 4 is a diagram of a state in which the first roller 40 and the driving roller 10 are opposed to each other after the state of FIG. 4 is rotated clockwise by a predetermined angle.

[0042] Fig. 20 It is a side cross-sectional view including the switching cam 50 of the secondary transfer unit 9 according to the present embodiment, and is a diagram showing a modified example in which the reference position of the first roller 40 is detected by the third position detection sensor S3 . DETAILED DESCRIPTION

[0043] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 is a schematic diagram showing the structure of an image forming apparatus 100 including a secondary transfer unit 9 of the present invention. Figure 2 yes Figure 1 An enlarged view of the vicinity of the image forming portion Pa in FIG.

[0044] Figure 1 The image forming apparatus 100 shown is a so-called tandem color printer having the following structure. Four image forming units Pa, Pb, Pc, and Pd are arranged from the upstream side in the conveying direction ( Figure 1 The image forming units Pa to Pd are sequentially arranged in the main body of the image forming apparatus 100. These image forming units Pa to Pd are arranged corresponding to images of four different colors (magenta, cyan, yellow and black), and sequentially form magenta, cyan, yellow and black images through the steps of charging, exposure, development and transfer.

[0045] In these image forming units Pa to Pd, photosensitive drums 1a, 1b, 1c, and 1d are provided for carrying visible images (toner images) of respective colors. Figure 1 The intermediate transfer belt 8 that rotates counterclockwise is disposed adjacent to each image forming unit Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially transferred to the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then are primarily transferred to a sheet S as an example of a recording medium in the secondary transfer unit 9. Furthermore, after being fixed to the sheet S in the fixing unit 13, the toner images are discharged from the main body of the image forming apparatus 100. While the photosensitive drums 1a to 1d are moving, the toner images formed on the photosensitive drums 1a to 1d are sequentially transferred to the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then are primarily transferred to a sheet S as an example of a recording medium in the secondary transfer unit 9. Figure 1 The photosensitive drum 1 a to 1 d performs image forming processing on each of the photosensitive drums 1 a to 1 d while rotating in the clockwise direction.

[0046] Paper S to which a toner image is transferred is stored in a paper cassette 16 at a lower portion of the main body of the image forming apparatus 100 and is conveyed to the secondary transfer unit 9 via a paper feed roller 12a and a resist roller pair 12b. The intermediate transfer belt 8 is mainly a seamless belt.

[0047] Next, the image forming units Pa to Pd will be described. The image forming unit Pa will be described in detail below, but since the image forming units Pb to Pd also have basically the same structure, their description will be omitted. Figure 2 As shown, around the photosensitive drum 1a, along the drum rotation direction ( Figure 2 A charging device 2a, a developing device 3a, and a cleaning device 7a are provided (in the clockwise direction of the photosensitive drum 1a), and a primary transfer roller 6a is provided across the intermediate transfer belt 8. In addition, a belt cleaning unit 19 is provided on the upstream side of the intermediate transfer belt 8 in the rotation direction relative to the photosensitive drum 1a, and the belt cleaning unit 19 is opposite to the tension roller 11 across the intermediate transfer belt 8.

[0048] Next, the image forming process of the image forming apparatus 100 will be described. When the user inputs the start of image formation, first, the main motor 60 (see Figure 8 ) The photosensitive drums 1a to 1d start rotating, and the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the charging rollers 20 of the charging devices 2a to 2d. Next, the surfaces of the photosensitive drums 1a to 1d are irradiated with light by a light beam (laser) emitted from the exposure device 5, and an electrostatic latent image corresponding to the image signal is formed on each photosensitive drum 1a to 1d.

[0049] The developing devices 3a to 3d are filled with a predetermined amount of magenta, cyan, yellow, and black toners, respectively. When the ratio of the toner in the two-component developer filled in each developing device 3a to 3d is lower than a predetermined value due to the formation of a toner image described later, the toner is replenished from the toner container 4a to 4d to each developing device 3a to 3d. The toner in the developer is supplied to the photosensitive drums 1a to 1d by the developing roller 21 of the developing device 3a to 3d, and is electrostatically attached to the photosensitive drums 1a to 1d. Thus, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 5 is formed.

[0050] Then, the primary transfer rollers 6a to 6d apply an electric field between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d at a predetermined transfer voltage, and the magenta, cyan, yellow and black toner images on the photosensitive drums 1a to 1d are primarily transferred to the intermediate transfer belt 8. In order to form a predetermined color image, these four color images are formed in a predetermined positional relationship. After that, in order to prepare for the formation of a new electrostatic latent image to be performed next, the toner remaining on the surface of the photosensitive drums 1a to 1d is removed by the cleaning blades 22 and the sliding friction rollers 23 of the cleaning devices 7a to 7d.

[0051] When the belt driving motor 61 (refer to Figure 8) rotates the driving roller 10 and the intermediate transfer belt 8 starts to rotate counterclockwise, the paper S is conveyed from the registration roller pair 12b to the secondary transfer unit 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and a color image is transferred. The paper S with the toner image transferred is conveyed to the fixing unit 13. The toner remaining on the surface of the intermediate transfer belt 8 is removed by the belt cleaning unit 19.

[0052] The paper S conveyed to the fixing section 13 is heated and pressed by the fixing roller pair 13a, and the toner image is fixed on the surface of the paper S, thereby forming a predetermined color image. The paper S with the color image formed thereon is divided into conveying directions by the branching section 14 that branches in multiple directions, and is discharged to the paper discharge tray 17 directly (or after being conveyed to the double-sided conveying path 18 for double-sided printing) by the discharge roller pair 15.

[0053] An image density sensor 25 is disposed at a position opposite to the driving roller 10 across the intermediate transfer belt 8. An optical sensor having a light emitting element composed of an LED or the like and a light receiving element composed of a photodiode or the like is generally used as the image density sensor 25. When the amount of toner attached to the intermediate transfer belt 8 is measured, when the measurement light is irradiated from the light emitting element to each patch image (reference image) formed on the intermediate transfer belt 8, the measurement light is incident on the light receiving element as light reflected by the toner and light reflected by the belt surface.

[0054] The reflected light from the toner and the belt surface includes specular reflected light and diffuse reflected light. The specular reflected light and diffuse reflected light are separated by the polarization splitting prism and then incident on different light receiving elements. Each light receiving element performs photoelectric conversion on the received specular reflected light and diffuse reflected light and transmits the received specular reflected light and diffuse reflected light to the control unit 90 (refer to Figure 8 ) outputs the output signal.

[0055] Then, the image concentration (colorant amount) and image position of the patch image are detected based on the characteristic changes of the output signals of the mirror reflected light and the diffuse reflected light, and compared with the predetermined reference concentration and reference position, and the characteristic value of the developing voltage, the exposure start position and time of the exposure device 5, etc. are adjusted, thereby performing concentration correction and color misalignment correction (calibration) for each color.

[0056] Figure 3 1 is a side cross-sectional view of the intermediate transfer unit 30 loaded in the image forming apparatus 100. Figure 3 As shown, the intermediate transfer unit 30 includes: an intermediate transfer belt 8 stretched between a downstream drive roller 10 and an upstream tension roller 11 ; first transfer rollers 6 a to 6 d contacting the photosensitive drums 1 a to 1 d via the intermediate transfer belt 8 ; and a pressure switching roller 34 .

[0057] Figure 32 is a side cross-sectional view of the intermediate transfer unit 30 mounted on the image forming apparatus 100. Figure 3 As shown, the intermediate transfer unit 30 includes: an intermediate transfer belt 8 stretched between a downstream drive roller 10 and an upstream tension roller 11 ; primary transfer rollers 6 a to 6 d contacting the photosensitive drums 1 a to 1 d via the intermediate transfer belt 8 ; and a pressure switching roller 34 .

[0058] A belt cleaning unit 19 is disposed opposite to the tension roller 11 to remove toner remaining on the surface of the intermediate transfer belt 8. A secondary transfer unit 9 is disposed in pressure contact with the driving roller 11 via the intermediate transfer belt 8 to form a secondary transfer roller nip N. The detailed structure of the secondary transfer unit 9 will be described later.

[0059] The intermediate transfer unit 30 includes a roller clutch mechanism 35, which includes a pair of supporting members (not shown) that support both ends of the shafts of the primary transfer rollers 6a to 6d and the pressure switching roller 34 so as to be rotatable and perpendicular to the traveling direction of the intermediate transfer belt 8 ( Figure 3 The roller clutch mechanism 35 can be switched to the following modes: the four primary transfer rollers 6a to 6d are respectively connected to the photosensitive drums 1a to 1d (see Figure 1) via the intermediate transfer belt 8. Figure 1 ) color mode in which the primary transfer roller 6d is pressed against the photosensitive drum 1d via the intermediate transfer belt 8; a black and white mode in which the primary transfer rollers 6a to 6d are pressed against the photosensitive drum 1d; and a retreat mode in which all four primary transfer rollers 6a to 6d are separated from the photosensitive drums 1a to 1d.

[0060] Figure 4 It is a perspective view of the secondary transfer unit 9 according to one embodiment of the present invention mounted in the image forming apparatus 100 . Figure 5 It is an enlarged perspective view showing the structure of one end side of the secondary transfer unit 9 according to the present embodiment. Figure 6 This is a perspective view of the periphery of the roller holder 47 of the secondary transfer unit 9 according to the present embodiment as viewed from the rear side. Figure 7 is a perspective view showing a driving mechanism of the secondary transfer unit 9 of this embodiment. Figure 4 and Figure 7 The description of the unit frame 9a is omitted. Figure 5 The unit frame 9a is shown in a transparent state.

[0061] like Figure 4 to Figure 7 As shown, the secondary transfer unit 9 includes a first roller 40 and a second roller 41 as secondary transfer rollers, a first bearing member 43 , a second bearing member 45 , a roller holder 47 , a switching cam 50 , and a roller switching motor 55 .

[0062] The first roller 40 and the second roller 41 are elastic rollers each having a core 40a, 41a laminated with an electrically conductive elastic layer 40b, 41b on its outer circumferential surface. The elastic layers 40b, 41b are made of, for example, ion conductive rubber such as ECO (epichlorohydrin rubber).

[0063] The axial length of the elastic layer 40b of the first roller 40 is 311 mm, corresponding to A3 size paper. The axial length of the elastic layer 41b of the second roller 41 is greater than that of the elastic layer 40b of the first roller 40. More specifically, the axial length of the elastic layer 41b is 325 mm, corresponding to 13 inch size paper.

[0064] A pair of first bearing members 43 are disposed at both ends of the first roller 40 in the axial direction to rotatably support the core shaft 40a. A pair of second bearing members 45 are disposed at both ends of the second roller 41 in the axial direction to rotatably support the core shaft 41a.

[0065] A pair of roller brackets 47 are arranged at both ends of the first roller 40 and the second roller 41 in the axial direction. The roller bracket 47 is roughly V-shaped when viewed from the side, and has a first bearing holding portion 47a, a second bearing holding portion 47b, and an insertion hole 47c. The first bearing holding portion 47a and the second bearing holding portion 47b respectively hold the first bearing member 43 and the second bearing member 45 so that they can slide. The insertion hole 47c is formed at the top of the V-shape, and the shaft 51 is inserted into the insertion hole 47c in a rotatable manner. The roller bracket 47 is formed of an insulating material such as a synthetic resin.

[0066] like Figure 5 As shown, a first coil spring 48 (first force applying member) is arranged between the first bearing holding portion 47a and the first bearing member 43. A second coil spring 49 (second force applying member) is arranged between the second bearing holding portion 47b and the second bearing member 45. The first roller 40 is urged in a direction away from the shaft 51 (a direction in which it is pressed against the drive roller 10) by the first coil spring 48, and the second roller 41 is urged in a direction away from the shaft 51 (a direction in which it is pressed against the drive roller 10) by the second coil spring 49.

[0067] like Figure 4 As shown, a first light shielding plate 51a is attached to the shaft 51, which shields the first position detection sensor S1 (see Fig. 9 ) can detect the rotation angle of the shaft 51. Figure 6 As shown, a second light shielding plate 47d is formed on one side surface in the rotation direction of the roller holder 47. The second light shielding plate 47d is formed at a position capable of shielding the detection portion of the second position detection sensor S2 disposed in the unit frame 9a.

[0068] The first shading plate 51a and the second shading plate 47d turn on or off the first position detection sensor S1 and the second position detection sensor S2 according to the rotation angle of the roller bracket 47 (shaft 51), thereby detecting the positions of the first roller 40 and the second roller 41 supported by the roller bracket 47. The position detection control of the first roller 40 and the second roller 41 will be described later.

[0069] A pair of switching cams 50 are arranged at both ends of the first roller 40 and the second roller 41 in the axial direction on the outside of the roller bracket 47. The switching cam 50 is fan-shaped when viewed from the side, and the main part of the fan (the vertex part where the two radii intersect) is fixed to the shaft 51. Figure 7 As shown, the roller switching motor 55 is connected to the shaft 51 via gears 52 and 53. The arrangement of the first roller 40 and the second roller 41 is switched by rotating the switching cam 50 together with the shaft 51. The switching control of the first roller 40 and the second roller 41 will be described later.

[0070] Figure 8 This is a block diagram showing an example of a control path of the image forming apparatus 100 equipped with the secondary transfer unit 9 according to the present embodiment. In addition, various controls are performed on each part of the apparatus based on the use of the image forming apparatus 100, so the control path of the entire image forming apparatus 100 becomes complicated. Here, the part of the control path necessary for the implementation of the present invention is mainly described.

[0071] The control unit 90 includes at least a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 as a read-only storage unit, a RAM (Random Access Memory) 93 as a readable and writable storage unit, a temporary storage unit 94 for temporarily storing image data, etc., a counter 95, and a plurality of (here, two) I / Fs (interfaces) 96 for sending control signals to various devices in the image forming apparatus 100 or receiving input signals from the operation unit 80. In addition, the control unit 90 can be arranged at any place inside the main body of the image forming apparatus 100.

[0072] The ROM 92 stores a control program for the image forming apparatus 100 and data such as numerical values ​​required for control that do not change during use of the image forming apparatus 100. The RAM 93 stores necessary data generated during control of the image forming apparatus 100 and data that becomes temporarily necessary for control of the image forming apparatus 100. In addition, the RAM 93 (or the ROM 92) stores a density correction table used for calibration, a threshold value of a paper size used for roller switching control described later, and the like. The counter 95 accumulates and counts the number of printed sheets.

[0073] In addition, the control unit 90 sends control signals to various parts and devices in the image forming apparatus 100 from the CPU 91 through the I / F 96. In addition, signals and input signals indicating the states of the various parts and devices are sent to the CPU 91 through the I / F 96. Examples of the various parts and devices controlled by the control unit 90 include the image forming units Pa to Pd, the exposure device 5, the primary transfer rollers 6a to 6d, the secondary transfer unit 9, the roller clutch mechanism 35, the main motor 60, the belt drive motor 61, the voltage control circuit 71, and the operation unit 80.

[0074] The image input unit 70 is a receiving unit that receives image data transmitted from a host device such as a computer to the image forming apparatus 100. The image signal input from the image input unit 70 is converted into a digital signal and then sent to the temporary storage unit 94.

[0075] The voltage control circuit 71 is connected to a charging voltage power supply 72, a developing voltage power supply 73, a transfer voltage power supply 74, and a cleaning voltage power supply 75, and operates the above-mentioned power supplies by output signals from the control unit 90. The above-mentioned power supplies are controlled by control signals from the voltage control circuit 71. The charging voltage power supply 72 applies a predetermined voltage to the charging roller 20 in the charging device 2a to 2d, the developing voltage power supply 73 applies a predetermined voltage to the developing roller 21 in the developing device 3a to 3d, and the transfer voltage power supply 74 applies a predetermined voltage to the primary transfer rollers 6a to 6d and the first roller 40 and the second roller 41 in the secondary transfer unit 9.

[0076] The operation unit 80 is provided with a liquid crystal display unit 81 and LEDs 82 indicating various states. The user operates the stop / clear button of the operation unit 80 to stop image formation, and operates the reset button to set various settings of the image forming apparatus 100 to default. The liquid crystal display unit 81 displays the state of the image forming apparatus 100 or displays the image formation status and the number of copies to be printed. Various settings of the image forming apparatus 100 are performed from the printer driver of the personal computer.

[0077] Next, the switching control and the position detection control of the first roller 40 and the second roller 41 in the secondary transfer unit 9 of the present embodiment will be described. Fig. 9 1 is a side cross-sectional view including the switching cam 50 of the secondary transfer unit 9 according to the present embodiment, and is a view showing a state in which the first roller 40 is arranged at a position where the secondary transfer roller nip portion N is formed. Fig.10 It is a top view of the switching cam 50 .

[0078] like Fig. 9As shown, a circular arc-shaped guide hole 63 is formed in the switching cam 50. A recess 64 is formed in the center of the radially outer peripheral portion of the guide hole 63. A first engaging portion 43a and a second engaging portion 45a engaging with the guide hole 63 are formed in the first bearing member 43 and the second bearing member 45, respectively.

[0079] like Fig.10 As shown, the recess 64 of the switching cam 50 is roughly trapezoidal in plan view, and has a bottom 64a corresponding to the upper side of the trapezoid and an inclined portion 64b corresponding to the hypotenuse of the trapezoid. By the rotation of the switching cam 50, the first engaging portion 43a of the first bearing member 43 and the second engaging portion 45a of the second bearing member 45 engage with or separate from the bottom 64a and the inclined portion 64b of the recess 64, thereby switching the contact state of the first roller 40 and the second roller 41 relative to the intermediate transfer belt 8 as described later. In addition, one side of the outer periphery of the switching cam 50 (the image forming apparatus 100 main body side, Fig.10 The left side of the device is extended along the tangential direction to form a protrusion 50a.

[0080] exist Fig. 9 In the state, the first engagement portion 43a of the first bearing member 43 engages with the bottom 64a of the recess 64. As a result, the first roller 40 is moved by the first coil spring 48 (see Figure 5 ) forms a secondary transfer roller nip N via the intermediate transfer belt 8 and the driving roller 10, and the first roller 40 and the driving roller 10 are driven to rotate. Figure 8 ) applies a transfer voltage of opposite polarity (here, negative polarity) to the toner to the first roller 40. Specifically, when the first roller 40 is arranged at Fig. 9 , a transfer voltage is applied via the first bearing component 43 electrically connected to the transfer voltage power supply 74.

[0081] In addition, the first light shielding plate 51a of the shaft 51 (see Figure 4 ) shields the detection part of the first position detection sensor S1 (turns on), and the first light shielding plate 47d of the roller bracket 47 shields the detection part of the second position detection sensor S2 (turns on). This state (S1 / S2 turned on) is set as the reference position (starting position) of the first roller 40. The rotation angle of the switching cam 50 is limited based on the rotation time of the switching cam 50 from the reference position, and the configuration and separation state of the first roller 40 are controlled.

[0082] With respect to the paper conveying direction, on the upstream side of the secondary transfer roller nip N ( Fig. 9The first pre-transfer guide 65 and the second pre-transfer guide 67 are arranged on the lower side of the sheet. The first pre-transfer guide 65 is supported by the unit frame 9a so that it can swing at the first fulcrum 65a. The second pre-transfer guide 67 is supported by the main frame (not shown) so that it can swing at the second fulcrum 67a. The first pre-transfer guide 65 and the second pre-transfer guide 67 are respectively supported along the paper width direction (with respect to the paper width direction). Fig. 9 Extending in a direction perpendicular to the paper surface).

[0083] Abutment pieces 65b are formed at both ends of the first pre-transfer guide 65 in the paper width direction to abut against the second pre-transfer guide 67. A second fulcrum 67a of the second pre-transfer guide 67 is provided with a support for the second pre-transfer guide 67 in the direction of approaching the first pre-transfer guide 65 ( Fig. 9 With this structure, the second transfer front guide 67 maintains a certain distance (the protruding height of the contact piece 65b) from the first transfer front guide 65 and follows the swing of the first transfer front guide 65. Fig. 9 In the state, the first transfer pre-guide 65 is arranged at a position (first guide position) where the sheet S can be guided toward the secondary transfer roller nip portion N.

[0084] Fig.11 This means that the switching cam 50 is Fig. 9 The state is rotated clockwise by a specified angle (here from Fig. 9 When the shaft 51 is rotated clockwise, the switching cam 50 also rotates together with the shaft 51. As a result, the swing end ( Fig. 9 The lower right end portion of the first roller 40 is pressed by the protrusion 50a of the switching cam 50 and swings in the clockwise direction. In addition, since the contact piece 65b of the first transfer front guide 65 presses the second transfer front guide 67, the second transfer front guide 67 also swings in the clockwise direction against the force of the torsion spring 68. In addition, although the first engaging portion 43a of the first bearing member 43 moves slightly from the bottom 64a of the recess 64 to the inclined portion 64b, the first roller 40 is pressed against the driving roller 10 via the intermediate transfer belt 8, and the state in which the secondary transfer roller gap N is formed is maintained.

[0085] Thus, the angles of the first transfer front guide 65 and the second transfer front guide 67 relative to the secondary transfer roller gap N change from Fig. 9Specifically, the angles of the first transfer front guide 65 and the second transfer front guide 67 toward the secondary transfer roller gap N (the angles relative to the tangent line passing through the secondary transfer roller gap N) are reduced (second guide position). Since the second guide position reduces the conveying load when guiding the paper S with strong elasticity, such as thick paper, to the secondary transfer roller gap N, it is a configuration that is conducive to the conveyance of the paper S with strong elasticity.

[0086] Fig.12 This means that the switching cam 50 is Fig.11 The state is rotated clockwise by a specified angle (here from Fig. 9 When the shaft 51 is rotated clockwise, the switching cam 50 also rotates together with the shaft 51. On the other hand, the roller bracket 47 is provided with a restriction rib 9b (see Figure 5 As a result, the first engaging portion 43a of the first bearing member 43 moves further radially inward from the inclined portion 64b of the recess 64, and the first bearing member 43 overcomes the first coil spring 48 (see Figure 5 ) moves in a direction approaching the shaft 51. As a result, the first roller 41 is in a state slightly (2 mm) separated from the intermediate transfer belt 8 (a first separated state).

[0087] If the first roller 40 is pressed against the driving roller 10 for a long time, the first roller 40 may bend and deform in the axial direction. Therefore, it is necessary to separate the first roller 40 from the intermediate transfer belt 8 (driving roller 10) after the operation is completed. Fig.12 The first separation state is shown.

[0088] In addition, the first light shielding plate 51a of the shaft 51 is withdrawn (disconnected) from the detection part of the first position detection sensor S1, and the second light shielding plate 47d of the roller bracket 47 continues to shield the detection part of the second position detection sensor S2 (on). Fig. 9 The detection status (S1 / S2 is on) Fig.12 When the detection state (S1 off / S2 on) of the first roller 40 is transferred, the movement from the reference position of the first roller 40 to the first separated state can be detected.

[0089] Fig.13 This means that the switching cam 50 is Fig.12 The state is further rotated clockwise by a specified angle (here from Fig. 9 When the shaft 51 is further rotated in the clockwise direction, the switching cam 50 is also further rotated in the clockwise direction together with the shaft 51. On the other hand, the roller bracket 47 is restrained by the limiting rib 9b (refer to Figure 5) restricts the clockwise rotation. As a result, the first engagement portion 43a of the first bearing member 43 moves from the recess 64, and the first bearing member 43 overcomes the first coil spring 48 (see Figure 5 ) further moves in the direction approaching the shaft 51. As a result, the second roller 41 is completely separated (6.5 mm) from the intermediate transfer belt 8 (second separation state). This second separation state is used only when switching from the first roller 40 to the second roller 41.

[0090] in addition, Fig.13 The detection states of the first position detection sensor S1 and the second position detection sensor S2 in Fig.12 The first separation state shown in FIG. 1 is the same as that in FIG. 1 (S1 off / S2 on). Therefore, when the image forming apparatus 100 is in the S1 off / S2 on state at startup, in order to distinguish the first separation state from the second separation state, the roller bracket 47 is rotated toward the main body side of the image forming apparatus 100 (counterclockwise) for a predetermined time. Then, if it is in the S1 / S2 on state, it is determined to be the first separation state, and if it is not in the S1 / S2 on state, it is determined to be the second separation state.

[0091] In addition, when returning the first roller 40 from the second separated state to the reference position, it is necessary to temporarily rotate the roller holder 47 and the switching cam 50 counterclockwise to switch to the reference position of the second roller 41 (see Fig.15 ) and then returns to the reference position of the first roller 40 (refer to Fig. 9 ).

[0092] Next, the procedure for switching the roller forming the secondary transfer roller nip N from the first roller 40 to the second roller 41 will be described. Fig.13 When the second separation state shown in FIG. 1 is rotated counterclockwise, the switching cam 50 also rotates counterclockwise together with the shaft 51. In addition, the first bearing member 43 is rotated counterclockwise by the first coil spring 48 (see FIG. 1 ). Figure 5 ) is applied in a direction away from the shaft 51, and the second bearing member 45 is forced by the second coil spring 49 (refer to Figure 5 ) is applied in a direction away from the shaft 51. Therefore, the first engaging portion 43a and the second engaging portion 45a are pressed against the peripheral edge portion of the radially outer side of the guide hole 63 of the switching cam 50. As a result, the roller bracket 47 also rotates counterclockwise together with the switching cam 50.

[0093] Then, when the roller bracket 47 rotates to the position where it is aligned with the restriction rib 9c (refer to Figure 5 ) when they are in contact, if Fig.14 As shown in FIG. 1 , the second roller 41 is arranged at a position opposite to the driving roller 10. Fig.14In the state, the first light shielding plate 51a of the shaft 51 is retracted (disconnected) from the detection part of the first position detection sensor S1, and the second light shielding plate 47d of the roller bracket 47 is retracted (disconnected) from the detection part of the second position detection sensor S2. Fig.13 The detection status (S1 off / S2 on) is Fig.14 When the detection state (S1 / S2 is off) is transferred, the movement of the second roller 41 to the position opposite to the driving roller 10 can be detected.

[0094] Fig.15 This means that the switching cam 50 is Fig.14 When the shaft 51 is rotated counterclockwise by a predetermined angle, the switching cam 50 also rotates together with the shaft 51. On the other hand, the roller bracket 47 is restrained by the limiting rib 9c (refer to Figure 5 As a result, the second engagement portion 45a of the second bearing member 45 moves to the bottom 64a of the recess 64, and the second bearing member 45 is moved by the second coil spring 49 (see Figure 5 ) moves in a direction away from the axis 51.

[0095] Thus, the second roller 41 is pressed against the driving roller 10 via the intermediate transfer belt 8 to form a secondary transfer roller nip N, and the second roller 41 and the driving roller 10 are driven to rotate. Figure 8 ) applies a transfer voltage of opposite polarity (here, negative polarity) to the toner to the second roller 41. Specifically, when the second roller 41 is arranged at Fig.15 When the transfer voltage is in the position, the transfer voltage is applied via the second bearing component 45 electrically connected to the transfer voltage power supply 74.

[0096] In addition, the first light shielding plate 51a of the shaft 51 shields the detection part of the first position detection sensor S1 (ON), and the second light shielding plate 47d of the roller bracket 47 retreats from the detection part of the second position detection sensor S2 (OFF). This state (S1 ON / S2 OFF) is set as the reference position (starting position) of the second roller 41. That is, when Fig.13 The detection status (S1 / S2 disconnected) Fig.14 When the detection state (S1 on / S2 off) of the second roller 41 is transferred, the movement of the second roller 41 to the reference position can be detected. Based on the rotation time of the switching cam 50 from the reference position, the rotation angle of the switching cam 50 is limited to control the configuration and separation state of the second roller 41.

[0097] The second roller 41 is arranged at the reference position. Fig.15 The arrangement of the first transfer front guide 65 and the second transfer front guide 67 is different from the arrangement of the first roller 40 at the reference position. Fig. 9 same.

[0098] Fig.16 It indicates that the switching cam 50 is Fig.15 The state is rotated counterclockwise by a specified angle (here from Fig.15 When the shaft 51 is rotated clockwise, the switching cam 50 also rotates together with the shaft 51. As a result, the swing end ( Fig. 9 The lower right end portion of the first transfer front guide 65 is pressed by the protrusion 50a of the switching cam 50 and swings in the clockwise direction. In addition, since the contact piece 65b of the first transfer front guide 65 presses the second transfer front guide 67, the second transfer front guide 67 also overcomes the force of the torsion spring 68 and swings in the clockwise direction. In addition, although the second engaging portion 45a of the second bearing member 45 moves slightly from the bottom 64a of the recess 64 to the inclined portion 64b, the second roller 41 is pressed against the driving roller 10 via the intermediate transfer belt 8, thereby maintaining the state in which the secondary transfer roller gap N is formed.

[0099] Thus, the angles of the first transfer front guide 65 and the second transfer front guide 67 relative to the secondary transfer roller gap N change from Fig.15 Specifically, the angle of the first transfer front guide 65 and the second transfer front guide 67 toward the secondary transfer roller gap N (relative to the angle of the tangent passing through the secondary transfer roller gap N) becomes a smaller configuration (second guide position), which becomes a configuration that is advantageous for guiding paper with strong elasticity, especially thick paper, toward the secondary transfer roller gap N.

[0100] Fig.17 This means that the switching cam 50 is further rotated counterclockwise by a predetermined angle (here, from Fig.15 When the shaft 51 is further rotated in the counterclockwise direction, the switching cam 50 is also further rotated in the counterclockwise direction together with the shaft 51. On the other hand, the roller bracket 47 is restrained by the limiting rib 9c (refer to Figure 5 As a result, the second engagement portion 45a of the second bearing member 45 moves from the bottom of the recess 64 to the inclined portion, and the first bearing member 45 overcomes the second coil spring 49 (see Figure 5 ) moves in a direction approaching the shaft 51. As a result, the second roller 41 is in a state slightly separated (2 mm) from the intermediate transfer belt 8 (a first separated state).

[0101] If the second roller 41 is pressed against the driving roller 10 for a long time, the second roller 41 may bend and deform in the axial direction. Therefore, it is necessary to separate the second roller 41 from the intermediate transfer belt 8 (driving roller 10) after the operation is completed. Fig.17Furthermore, when calibration is performed while the second roller 41 is in use, the second roller 41 is set to the first separated state so that the reference image formed on the intermediate transfer belt 8 does not adhere to the second roller 41. In addition, when calibration is performed while the second roller 41 is set to the first separated state, the reference image can be formed in the center portion in the width direction of the intermediate transfer belt 8.

[0102] In addition, the first light shielding plate 51a of the shaft 51 is withdrawn (disconnected) from the detection portion of the first position detection sensor S1, and the second light shielding plate 47d of the roller bracket 47 continues to be withdrawn (disconnected) from the detection portion of the second position detection sensor S2. Fig.16 The detection status (S1 on / S2 off) is Fig.17 When the detection state (S1 / S2 is disconnected) is transferred, the movement of the second roller 41 from the reference position to the first separated state can be detected.

[0103] Fig.18 This means that the switching cam 50 is Fig.17 The state is further rotated counterclockwise by a specified angle (here from Fig.14 When the shaft 51 is further rotated in the counterclockwise direction, the switching cam 50 is also further rotated in the counterclockwise direction together with the shaft 51. On the other hand, the roller bracket 47 is restrained by the limiting rib 9c (refer to Figure 5 As a result, the second engagement portion 45a of the second bearing member 45 moves from the recess 64, and the second bearing member 45 overcomes the second coil spring 49 (see Figure 5 ) moves in a direction closer to the shaft 51. As a result, the second roller 41 is completely separated (6.5 mm) from the intermediate transfer belt 8 (second separation state). This second separation state is used only when switching from the second roller 41 to the first roller 40.

[0104] in addition, Fig.18 The detection states of the first position detection sensor S1 and the second position detection sensor S2 in Fig.17 Therefore, when the image forming apparatus 100 is in the S1 / S2 off state at startup, the roller holder 47 is rotated toward the double-sided conveying path 18 side (clockwise) for a predetermined time in order to distinguish the first separation state from the second separation state. Then, if it is in the S1 on / S2 off state, it is determined to be the first separation state, and if it is not in the S1 on / S2 off state, it is determined to be the second separation state.

[0105] In addition, when returning the second roller 41 from the second separated state to the reference position, the roller holder 47 and the switching cam 50 need to be temporarily rotated clockwise to switch to the reference position of the first roller 40 (see Fig. 9 ) and then returns to the reference position of the second roller 41 (refer to Fig.15 ).

[0106] When the roller forming the secondary transfer roller nip N is switched from the second roller 41 to the first roller 40, the switching cam 50 is moved from Fig.18 Thus, the switching cam 50 and the roller bracket 47 also rotate clockwise by a predetermined angle, and when the roller bracket 47 rotates to abut against the limiting rib 9b, the first roller 40 and the driving roller 10 are opposite to each other. Fig.19 When the switching cam 50 is Fig.19 When the state is further rotated clockwise by a predetermined angle, the first roller 40 is configured at the reference position. Fig. 9 Next, by repeating the above steps, the first roller 40 and the second roller 41 are switched.

[0107] According to the structure of this embodiment, when the sheet S is smaller than a predetermined size (here, A3 size), the first roller 40 having the elastic layer 40b with a small axial length is arranged at the reference position. Thus, when a reference image is formed outside the image area in the width direction of the intermediate transfer belt 8 (outside in the axial direction of the first roller 40) during image formation for calibration, the reference image formed on the intermediate transfer belt 8 does not contact the first roller 40. Therefore, calibration can be performed during image formation, and image quality can be improved without reducing image processing efficiency (productivity).

[0108] Furthermore, it is possible to effectively suppress the back surface of the paper S from being contaminated by the toner attached to the first roller 40 adhering to the paper S. Furthermore, since it is not necessary to perform a cleaning operation to return the toner attached to the first roller 40 to the intermediate transfer belt 8, the printing waiting time can also be shortened.

[0109] On the other hand, when the paper S is larger than the specified size (here, 13 inches), the second roller 41 having the elastic layer 41b with a large axial length is arranged at the reference position. This allows the toner image to be reliably transferred to both ends of the large paper S in the width direction.

[0110] Furthermore, in the present embodiment, when the first roller 40 or the second roller 41 is arranged at the reference position, the first transfer front guide 65 is arranged at the first guide position capable of guiding the sheet S to the secondary transfer roller gap N by the rotation of the switching cam 50. Thus, the positional relationship of the first transfer front guide 65 relative to the secondary transfer roller gap N can be maintained when the first roller 40 and the second roller 41 are switched, and the sheet S can be smoothly guided to the secondary transfer roller gap N.

[0111] In addition, by rotating the switching cam 50, the first roller 40 or the second roller 41 can be maintained in the state of being arranged at the reference position, and the first pre-transfer guide 65 can be selectively arranged at the first guide position and the second guide position. Therefore, when the paper S is a paper with strong elasticity such as thick paper, the conveying load of the paper S can be reduced by arranging the first pre-transfer guide 65 at the second guide position.

[0112] Furthermore, the first transfer front guide 65 contacts the second transfer front guide 67 via the contact piece 65b, and the second transfer front guide 67 is urged by the torsion spring 68 toward the first transfer front guide 65. As a result, the first transfer front guide 65 is selectively arranged at the first guide position and the second guide position while maintaining a certain interval with the second transfer front guide 67. Thus, the positional relationship between the first transfer front guide 65 and the second transfer front guide 67 can be easily adjusted.

[0113] Furthermore, in the present embodiment, the separation position of the first roller 40 and the second roller 41 can be switched between a first separation state in which the separation distance from the intermediate transfer belt 8 is small and a second separation state in which the separation distance is large. Thus, when the first roller 40 and the second roller 41 are separated from the driving roller 10 at the end of the operation in order to prevent deformation of the first roller 40 and the second roller 41, when calibration is performed during use of the second roller 41, the first roller 40 and the second roller 41 are set to the first separation state, thereby shortening the time until they are arranged at the reference position for forming the second transfer roller nip N. Therefore, the reduction in image processing efficiency (productivity) accompanying the movement of the first roller 40 and the second roller 41 can be suppressed to a minimum.

[0114] Furthermore, in this embodiment, one roller switching motor 55 can be used to drive the roller bracket 47 and the switching cam 50. This simplifies the driving mechanism and driving control compared to the case where different motors are used to drive the roller bracket 47 and the switching cam 50, and contributes to the cost reduction and compactness of the image forming apparatus 100.

[0115] In addition, the present invention is not limited to the above-mentioned embodiment, and various changes can be implemented within the scope of the main purpose of the present invention. For example, the shape and size of the first roller 40, the second roller 41, the roller bracket 47, the switching cam 50, etc. constituting the secondary transfer unit 9 are only examples, and can be arbitrarily changed within the scope that does not hinder the effect of the present invention.

[0116] Furthermore, in the above-described embodiment, the first position detection sensor S1 and the second position detection sensor S2 are used to limit the rotation angle of the switching cam 50 and detect the arrangement and separation state of the first roller 40 and the second roller 41. However, for example, Fig. 20 As shown, a third position detection sensor S3 may be provided in the unit frame 9a in addition to the second position detection sensor S2, and a third light shielding plate 47e may be provided in the roller bracket 47. According to this configuration, the third light shielding plate 47 shields (turns on) the detection portion of the third position detection sensor S3 as the roller bracket 47 rotates, thereby making it possible to easily detect the reference position of the first roller 40.

[0117] In addition, in the above-mentioned embodiment, an intermediate transfer type image forming device 100 having a secondary transfer unit 9 is illustrated, and the secondary transfer unit 9 transfers the colorant image once transferred to the intermediate transfer belt 8 to the paper S for a second time, but it can also be similarly applied to a transfer unit mounted on a direct transfer type image forming device that directly transfers the colorant image formed on the photosensitive drum to the paper.

[0118] The present invention can be applied to an image forming device having a transfer unit for transferring a toner image formed on an image carrier to a recording medium. By utilizing the present invention, it is possible to provide a transfer unit that can switch two transfer rollers that are selectively pressed against an image carrier with a simple structure and can also maintain a positional relationship with a pre-transfer guide, and an image forming device having the transfer unit.

Claims

1. A transfer unit, characterized in that: The transfer unit includes a transfer roller having a core shaft and an elastic layer stacked on the outer peripheral surface of the core shaft, the elastic layer is pressed against the image carrier to form a transfer roller gap, and the transfer unit transfers the toner image formed on the image carrier to the recording medium passing through the transfer roller gap. The transfer unit comprises: a first roller as the transfer roller and a second roller having a greater axial length than the first roller for the elastic layer; a first bearing member rotatably supporting the first roller; a second bearing member rotatably supporting the second roller; A roller bracket having a first bearing holding portion and a second bearing holding portion, wherein the first bearing holding portion and the second bearing holding portion respectively hold the first bearing component and the second bearing component so as to be able to slide in a direction approaching or separating from the image carrier; A first force applying member is disposed between the first bearing holding portion and the first bearing member, and applies force to the first bearing member in a direction approaching the image carrier; A second force applying member is disposed between the second bearing holding portion and the second bearing member, and applies force to the second bearing member in a direction approaching the image carrier; A switching cam having a guide hole for engaging with a first engaging portion formed on the first bearing component and a second engaging portion formed on the second bearing component; a driving mechanism for rotationally driving the roller bracket and the switching cam; and The first pre-transfer guide is swingably supported by the unit frame on the upstream side of the transfer roller nip portion with respect to the conveying direction of the recording medium. By rotating the roller holder, one of the first roller and the second roller is arranged to face the image carrier, and By rotating the switching cam, the engagement positions of the first engagement portion and the second engagement portion in the guide hole are changed, and the first roller or the second roller arranged opposite to the image carrier is selectively arranged at a reference position where the transfer roller gap is formed by pressing against the image carrier and at a separation position where the transfer roller is separated from the image carrier. When the first roller or the second roller is arranged at the reference position, the first pre-transfer guide is arranged at a first guide position capable of guiding the recording medium to the transfer roller nip portion by the rotation of the switching cam.

2. The transfer unit according to claim 1, characterized in that: When the first roller or the second roller is configured at the reference position, the first pre-transfer guide is selectively configured at the first guide position and a second guide position whose angle relative to the tangent line passing through the transfer roller gap is smaller than that of the first guide position through the rotation of the switching cam.

3. The transfer unit according to claim 2, characterized in that: The first pre-transfer guide has a contact piece that contacts with a second pre-transfer guide that is arranged to face the first pre-transfer guide and is capable of swinging. The second pre-transfer guide is urged by a third urging member toward the first pre-transfer guide, and the first pre-transfer guide is selectively arranged at the first guide position and the second guide position while maintaining a certain interval with the second pre-transfer guide.

4. The transfer unit according to claim 3, characterized in that: The switching cam is fan-shaped and has a protrusion extending along a tangential direction on one side of the outer peripheral edge. When the first pre-transfer guide is arranged at the first guide position by the force of the third force applying member, as the switching cam rotates, the swing end of the first pre-transfer guide is pressed by the protrusion and moves toward the second guide position against the force of the third force applying member.

5. The transfer unit according to any one of claims 2 to 4, characterized in that: The transfer unit comprises: a plurality of position detection sensors for detecting the positions of the roller bracket and the switching cam in the rotational direction; and a control unit, controlling the driving mechanism, The control unit controls the driving mechanism based on the detection results of the plurality of position detection sensors to configure either the first roller or the second roller opposite to the image carrier, and selectively configures the first roller or the second roller opposite to the image carrier at the reference position and the separation position.

6. The transfer unit according to claim 5, characterized in that: The control unit detects movement of the first pre-transfer guide from the first guide position to the second guide position based on a rotation time of the switching cam from a state in which one of the first roller and the second roller is arranged at the reference position.

7. The transfer unit according to any one of claims 1 to 4, characterized in that: The switching cam has a recess formed on a peripheral edge portion radially outside the guide hole, and the first engaging portion or the second engaging portion is engaged with the recess to arrange the first roller or the second roller arranged to face the image carrier at the reference position.

8. The transfer unit according to claim 7, characterized in that: The recessed portion is trapezoidal in plan view, and the first roller or the second roller is set to a first separation state in which the roller is separated from the image carrier by a predetermined distance by engaging the first engaging portion or the second engaging portion with the inclined portion of the recessed portion, and the first roller or the second roller is set to a second separation state in which the separation distance is larger than that of the first separation state by separating the first engaging portion or the second engaging portion from the recessed portion.

9. The transfer unit according to any one of claims 1 to 4, characterized in that: The transfer unit comprises: A shaft fixed at the rotation center of the switching cam; and The roller switching motor causes the shaft to rotate, The roller holder is rotatably supported by the shaft, and the shaft is rotated by using the roller switching motor to rotate the switching cam and the roller holder.

10. An image forming device, characterized in that: include: The plurality of image forming units form the toner images of different colors; An endless intermediate transfer belt as the image carrier moves along the image forming section; a plurality of primary transfer members disposed opposite to the photosensitive drums disposed in the respective image forming units with the intermediate transfer belt interposed therebetween, and primarily transferring the toner images formed on the photosensitive drums to the intermediate transfer belt; and The secondary transfer unit as the transfer unit according to any one of claims 1 to 9 secondarily transfers the toner image primarily transferred onto the intermediate transfer belt onto the recording medium.

Images