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, a second roller, a first bearing component, a second bearing component, a roller bracket, a first force-applying component, a second force-applying component, a first switching cam, a second switching cam and a driving mechanism. The first switching cam and the second switching cam respectively have a first guide hole and a second guide hole that engage with a first engaging portion formed on the first bearing component and a second engaging portion formed on the second bearing component. By rotating the roller bracket, either the first roller or the second roller is arranged opposite to the image carrier, and by rotating the first switching cam and the second switching cam, the engaging position of the first engaging portion and the second engaging portion is changed, and the first roller or the second roller is selectively arranged at a reference position and a separation position that are pressed against the image carrier.

Description

Technical Field

[0001] The present invention relates to 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 an image forming apparatus including the transfer unit, and more particularly to a mechanism for switching the arrangement of a plurality of transfer members. 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 including the transfer unit, which can realize switching of two transfer rollers selectively brought into pressure contact with an image carrier with a simple structure.

[0007] The transfer unit of the first structure of the present invention is characterized in that:

[0008] The transfer roller comprises a core shaft and an elastic layer laminated on the outer peripheral surface of the core shaft, wherein 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.

[0009] The transfer unit comprises:

[0010] a first roller as the transfer roller and a second roller having a greater axial length than the first roller for the elastic layer;

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

[0012] a second bearing member rotatably supporting the second roller;

[0013] 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;

[0014] 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;

[0015] 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;

[0016] A first switching cam has a first guide hole for engaging with a first engaging portion formed on the first bearing member;

[0017] A second switching cam has a second guide hole for engaging with a second engaging portion formed on the second bearing member; and

[0018] a driving mechanism for rotating the roller bracket, the first switching cam and the second switching cam,

[0019] By rotating the roller holder, one of the first roller and the second roller is arranged to face the image carrier, and

[0020] The engaging position of the first engaging portion in the first guide hole and the engaging position of the second engaging portion in the second guide hole are changed by rotating the first switching cam and the second switching cam, and the first roller or the second roller arranged opposite to the image carrier is selectively arranged at a reference position at which the transfer roller gap is formed by being pressed against the image carrier and at a separation position at which the transfer roller is separated from the image carrier.

[0021] In addition, the present invention provides an image forming device, comprising:

[0022] The plurality of image forming units form the toner images of different colors;

[0023] An endless intermediate transfer belt as the image carrier moves along the image forming section;

[0024] 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

[0025] The secondary transfer unit as the transfer unit of the above configuration secondarily transfers the toner image primarily transferred onto the intermediate transfer belt onto the recording medium.

[0026] According to the first structure of the present invention, by using a simple structure including a roller holder, a first switching cam, and a second switching cam, it is possible to arrange either the first roller or the second roller opposite to the image carrier, and to selectively arrange the first roller or the second roller opposite to the image carrier at a reference position for forming a transfer roller gap and at a separation position for separating from the image carrier. In addition, compared with a structure in which the arrangement of the first roller and the second roller is switched using a single switching cam, the rotation angle of the switching cam can be reduced, and therefore, it is not necessary to increase the space required for the rotation of the switching cam, and the transfer unit can be made compact.

[0027] 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

[0028] Figure 1 1 is a schematic diagram showing the internal structure of an image forming apparatus 100 including the secondary transfer unit 9 of the present invention.

[0029] Figure 2 yes Figure 1 An enlarged view of the vicinity of the image forming portion Pa in FIG.

[0030] Figure 3 It is a side cross-sectional view of the intermediate transfer unit 30 mounted in the image forming apparatus 100 .

[0031] 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 .

[0032] Figure 5 It is an enlarged perspective view showing the structure of the roller holder 47 of the secondary transfer unit 9 according to the present embodiment.

[0033] Figure 6 yes Figure 4 A partially enlarged view of one end side of the secondary transfer unit 9 in FIG.

[0034] Figure 7 It is a perspective view showing the second bearing member 45 and the second switching cam 51 on one end side of the secondary transfer unit 9 .

[0035] Figure 8 It is a perspective view showing the first bearing member 43 and the first switching cam 50 on the other end side of the secondary transfer unit 9 .

[0036] Fig. 9 This is a perspective view of the periphery of the roller holder 47 of the secondary transfer unit 9 as viewed from the axial inner side.

[0037] Fig.10 It is a perspective view showing a driving mechanism of the secondary transfer unit 9 according to the present embodiment.

[0038] Fig.11 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.

[0039] Fig.12 It is a side cross-sectional view including the first switching cam 50 of the secondary transfer unit 9 of 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 roller nip N as viewed from the axial inner side.

[0040] Fig.13 It is a side cross-sectional view including the second switching cam 51 of the secondary transfer unit 9 of 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 roller nip N as viewed from the axially outer side.

[0041] Fig.14 3 is a top view of the first switching cam 50 .

[0042] Fig.15 3 is a top view of the second switching cam 51 .

[0043] Fig.16 This means that the first switching cam 50 is Fig.12 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.

[0044] Fig.17 This means that the first switching cam 50 is Fig.16FIG. 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.

[0045] Fig.18 1 is a side cross-sectional view including the second switching cam 51 of the secondary transfer unit 9 according to the present embodiment, and is a view showing a state in which the second roller 41 is arranged at a reference position for forming the secondary transfer nip portion N. FIG.

[0046] Fig.19 This means that the second switching cam 51 is Fig.18 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.

[0047] Fig. 20 This means that the second switching cam 51 is Fig.19 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.

[0048] Fig.21 The figure includes a side cross-sectional view of the second switching cam 51 of the secondary transfer unit 9 of the present embodiment and is a diagram of a modified example in which the reference position of the second roller 41 is detected by the third position detection sensor S3 . DETAILED DESCRIPTION

[0049] 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.

[0050] 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.

[0051] 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 1The 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.

[0052] 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.

[0053] 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.

[0054] 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 Fig.11 ) 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.

[0055] 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.

[0056] 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.

[0057] When the belt driving motor 61 (refer to Fig.11 ) 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.

[0058] 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.

[0059] 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.

[0060] 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 Fig.11 ) outputs the output signal.

[0061] 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.

[0062] Figure 3 2 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 .

[0063] 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 via the intermediate transfer belt 8 on the driving roller 11 to form a secondary transfer nip N. The detailed structure of the secondary transfer unit 9 will be described later.

[0064] 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.

[0065] 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 5It 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 yes Figure 4 A partially enlarged view of one end side of the secondary transfer unit 9 in FIG. Figure 7 It is a perspective view showing the second bearing member 45 and the second switching cam 51 on one end side of the secondary transfer unit 9 . Figure 8 It is a perspective view showing the first bearing member 43 and the first switching cam 50 on the other end side of the secondary transfer unit 9 . Fig. 9 This is a perspective view of the periphery of the roller holder 47 of the secondary transfer unit 9 as viewed from the axial inner side. Fig.10 is a perspective view showing a driving mechanism of the secondary transfer unit 9 of this embodiment. Figure 4 and Figure 6 to Figure 10 The description of the unit frame 9a is omitted. Fig. 9 The description of the first switching cam 50 is omitted. Figure 5 The unit frame 9a is shown in a transparent state.

[0066] like Figures 4 to 10 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 first switching cam 50 , a second switching cam 51 , and a roller switching motor 55 .

[0067] 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).

[0068] 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.

[0069] 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.

[0070] 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 52 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.

[0071] like Figure 5 As shown, a first coil spring 48 is arranged between the first bearing holding portion 47a and the first bearing member 43. A second coil spring 49 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 52 (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 52 (a direction in which it is pressed against the drive roller 10) by the second coil spring 49.

[0072] like Figure 4 , Figure 6 and Figure 8 As shown, a first light shielding plate 52a is attached to the shaft 52 to shield the first position detection sensor S1 (see Fig.12 ) can detect the rotation angle of the shaft 52. Fig. 9 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.

[0073] The first shading plate 52a 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 52), 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.

[0074] A pair of first switching cams 50 are arranged on the inner side of the roller bracket 47 at both ends of the first roller 40 and the second roller 41 in the axial direction. A pair of second switching cams 51 are arranged on the outer side of the roller bracket 47 at both ends of the first roller 40 and the second roller 41 in the axial direction. The first switching cam 50 and the second switching cam 51 are partially cut out from the side, and the main part of the fan (the vertex part where two radii intersect) is fixed to the shaft 52.

[0075] like Fig.10As shown, the roller switching motor 55 is connected to the shaft 52 via gears 53 and 54. The first and second switching cams 50 and 51 are rotated together with the shaft 52 to switch the arrangement of the first and second rollers 40 and 41. The switching control of the first and second rollers 40 and 41 will be described later.

[0076] Fig.11 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.

[0077] 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.

[0078] 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. The counter 95 accumulates and counts the number of printed copies.

[0079] 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 image input unit 70, the voltage control circuit 71, and the operation unit 80.

[0080] The image input unit 70 is a receiving unit that receives image data transmitted from a host device such as a personal computer to the image forming apparatus 100 . The image signal input by the image input unit 70 is converted into a digital signal and then transmitted to the temporary storage unit 94 .

[0081] The voltage control circuit 71 is connected to the charging voltage power supply 72, the developing voltage power supply 73, and the transfer voltage power supply 74, and operates the above-mentioned power supplies by the output signal from the control unit 90. According to the control signal 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.

[0082] 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.

[0083] 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.12 It is a side cross-sectional view including the first switching cam 50 of the secondary transfer unit 9 of 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 roller nip N as viewed from the axial inner side. Fig.13 1 is a side cross-sectional view of the second switching cam 51 of the secondary transfer unit 9 of the present embodiment, and is a view showing a state in which the first roller 40 is arranged at a reference position for forming the secondary transfer roller gap N, as viewed from the axially outer side. Fig.12 and Fig.13 In the same way, Fig.13 The diagram shows Fig.12 The opposite side ( Figure 4 The structure is on the front right side of the paper.

[0084] like Fig.12 As shown, a first guide hole 63 is formed in the first switching cam 50. A recess 64 is formed in the peripheral portion of the radially outer side of the first guide hole 63. A first engaging portion 43a that engages with the first guide hole 63 is formed in the first bearing member 43. Fig.13As shown, the second switching cam 51 has a second guide hole 65 formed therein. A recessed portion 66 is formed at the radially outer peripheral edge of the second guide hole 65. The second bearing member 45 has a second engaging portion 45a that engages with the second guide hole 65 formed therein.

[0085] Fig.14 and Fig.15 1 and 2 are top views of the first switching cam 50 and the second switching cam 51, respectively. Fig.14 As shown, the recessed portion 64 of the first switching cam 50 has a bottom portion 64a recessed to the outermost radial side and an inclined portion 64b inclined from the bottom portion 64a to the inner radial side. Fig.12 ) is engaged with the bottom 64a or the inclined portion 64b of the recess 64 or is separated from the recess 64, thereby being able to switch the contact state of the first roller 40 with respect to the intermediate transfer belt 8 as described later.

[0086] like Fig.15 As shown, the second switching cam 51 is a shape that is an inverted version of the first switching cam 50. The recessed portion 66 of the second switching cam 51 has a bottom portion 66a that is recessed to the outermost radial side, and an inclined portion 66b that is inclined from the bottom portion 66a to the inner radial side. Fig.13 ) is engaged with the bottom 66a or the inclined portion 66b of the recess 66 or is separated from the recess 66, thereby being able to switch the contact state of the second roller 41 with respect to the intermediate transfer belt 8 as described later.

[0087] exist Fig.12 and Fig.13 In the state, the first engagement portion 43a of the first bearing member 43 is engaged with the bottom 64a of the recess 64. In addition, the second engagement portion 45a of the second bearing member 45 is separated from the recess 66. 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. Fig.11 ) 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.12 and Fig.13 When the transfer voltage is in the position, the transfer voltage is applied via the first bearing component 43 electrically connected to the transfer voltage power supply 74.

[0088] In addition, the first light shielding plate 52a of the shaft 52 (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 first switching cam 50 is limited based on the rotation time of the first switching cam 50 rotating from the reference position, and the configuration and separation state of the first roller 40 are controlled.

[0089] Fig.16 This means that the first switching cam 50 is Fig.12 The state is rotated clockwise by a specified angle (here from Fig.12 When the shaft 52 is rotated clockwise, the first switching cam 50 also rotates together with the shaft 52. 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 from the bottom 64a of the recess 64 to the inclined portion 64b, and the first bearing member 43 overcomes the first coil spring 48 (see Figure 5 ) in the direction approaching the shaft 52. As a result, the first roller 40 is slightly separated (2 mm) from the intermediate transfer belt 8 (first separation state). In addition, the second switching cam 51 is also rotated clockwise by the same angle by the rotation of the shaft 52, but the second engaging portion 45a of the second bearing member 45 is maintained in a state of being separated from the recessed portion 66.

[0090] 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.16 The first separation state is shown.

[0091] In addition, the first light shielding plate 52a of the shaft 52 is withdrawn from the detection part of the first position detection sensor S1 (off), 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.12 The detection status (S1 / S2 is on) Fig.16 When the detection state (S1 off / S2 on) of the first roller 40 is transferred, the movement of the first roller 40 from the reference position to the first separated state can be detected.

[0092] Fig.17 This means that the first switching cam 50 is Fig.16 The state is further rotated clockwise by a specified angle (here from Fig.12When the shaft 52 is further rotated in the clockwise direction, the first switching cam 50 is also further rotated in the clockwise direction together with the shaft 52. 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 52. As a result, the first roller 40 is in a state (second separation state) completely separated (6.5 mm) from the intermediate transfer belt 8. This second separation state is used only when switching from the first roller 40 to the second roller 41.

[0093] in addition, Fig.17 The detection states of the first position detection sensor S1 and the second position detection sensor S2 in Fig.16 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.

[0094] 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 first switching cam 50 and the second switching cam 51 counterclockwise to switch to the reference position of the second roller 41 (see Fig.18 ) and then returns to the reference position of the first roller 40 (refer to Fig.12 ).

[0095] 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.17 When the second separation state shown in FIG. 1 is rotated counterclockwise, the first switching cam 50 and the second switching cam 51 also rotate counterclockwise together with the shaft 52. 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 52, 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 52. Therefore, the first engaging portion 43a is pressed against the peripheral edge portion of the radially outer side of the first guide hole 63 of the first switching cam 50. In addition, the second engaging portion 45a is pressed against the peripheral edge portion of the radially outer side of the second guide hole 65 of the second switching cam 51. As a result, the roller bracket 47 also rotates counterclockwise together with the first switching cam 50 and the second switching cam 51.

[0096] Fig.18 1 is a side cross-sectional view including the second switching cam 51 of the secondary transfer unit 9 of the present embodiment, and is a view showing a state where the second roller 41 is arranged at a reference position for forming the secondary transfer roller nip portion N. Fig.18 and the following Figures 19 to 21 In the embodiment, the positional relationship between the first roller 40 and the second roller 41 relative to the driving roller 10 is Fig.16 , Fig.17 The same way shows with Fig.13 Same side structure.

[0097] When the roller bracket 47 rotates to the position close to the restriction rib 9c (refer to Figure 5 ) abuts, the second roller 41 is arranged at a position opposite to the driving roller 10. In addition, the second engagement portion 45a of the second bearing member 45 moves to the bottom 66a of the recess 66, and the second bearing member 45 is connected to the second coil spring 49 (see Figure 5 ) moves in a direction away from the axis 52.

[0098] 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. Fig.11 ) 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.18 , a transfer voltage is applied via the second bearing member 45 electrically connected to the transfer voltage power supply 74. In addition, the first switching cam 50 also rotates clockwise by a predetermined angle due to the rotation of the shaft 52, but the first engagement portion 43a of the first bearing member 43 is separated from the recess 64.

[0099] In addition, the first light shielding plate 52a of the shaft 52 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.17 The detection status (S1 off / S2 on) is Fig.18When 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 second switching cam 51 from the reference position, the rotation angle of the second switching cam 51 is limited to control the configuration and separation state of the second roller 41.

[0100] Fig.19 This means that the second switching cam 51 is Fig.18 The state is rotated counterclockwise by a specified angle (here from Fig.18 When the shaft 52 is rotated counterclockwise, the second switching cam 51 also rotates counterclockwise together with the shaft 52. 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 66a of the recess 66 to the inclined portion 66b, and the second bearing member 45 overcomes the second coil spring 49 (see Figure 5 ) moves in a direction approaching the shaft 52. 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.19 Furthermore, 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 52a of the shaft 52 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.18 The detection status (S1 on / S2 off) is Fig.19 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. 20 This means that the second switching cam 51 is Fig.19 The state is further rotated counterclockwise by a specified angle (here from Fig.18When the shaft 52 is further rotated in the counterclockwise direction, the second switching cam 51 is also further rotated in the counterclockwise direction together with the shaft 52. 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 66, and the second bearing member 45 overcomes the second coil spring 49 (see Figure 5 ) moves in a direction closer to the shaft 52. 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. 20 The detection states of the first position detection sensor S1 and the second position detection sensor S2 in Fig.19 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 the second roller 41 is returned to the reference position from the second separated state, the roller holder 47 and the second switching cam 51 need to be temporarily rotated clockwise to switch to the reference position of the first roller 40 (see Fig.12 ) and then returns to the reference position of the second roller 41 (refer to Fig.18 ).

[0106] When the roller forming the secondary transfer roller nip N is switched from the second roller 41 to the first roller 40, the shaft 52 is moved from Fig. 20 The first roller 40 is rotated in the clockwise direction by a predetermined angle in the second separation state shown. As a result, the first switching cam 50, the second switching cam 51 and the roller bracket 47 are also rotated in the clockwise direction by a predetermined angle. When the roller bracket 47 rotates to abut against the limiting rib 9b, the first roller 40 and the driving roller 10 are in a state of facing each other. In addition, the first engaging portion 43a of the first bearing member 43 moves to the bottom 64a of the recess 64, and the first roller 40 is arranged in the reference position. Fig.12 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, by using a simple structure of a roller bracket 47 and a first switching cam 50 and a second switching cam 51, either the first roller 40 or the second roller 41 can be arranged opposite to the driving roller 10, and the first roller 40 or the second roller 41 arranged opposite to the driving roller 10 can be selectively arranged at a reference position for forming a secondary transfer roller gap N and a separation position for separating from the intermediate transfer belt 8.

[0108] For example, when the sheet S is smaller than a predetermined size (here, A3 size), the first roller 40 having the elastic layer 40a 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).

[0109] 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 . 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 be shortened.

[0110] On the other hand, when the paper S is larger than a predetermined size (here, 13 inches), the second roller 41 having the elastic layer 41a with a large axial length is arranged at the reference position. Thus, the toner image can be reliably transferred to both ends of the paper S in the width direction.

[0111] Furthermore, by switching the configuration of the first roller 40 using the first switching cam 50 and switching the configuration of the second roller 41 using the second switching cam 51, the rotation angle of the switching cam can be reduced (set to 1 / 2) compared to a structure in which one switching cam is used to switch the configurations of the first roller 40 and the second roller 41. Therefore, there is no need to increase the space required for the rotation of the first switching cam 50 and the second switching cam 51, and the secondary transfer unit 9 can be made compact.

[0112] 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, the first roller 40 and the second roller 41 are set to the first separation state when calibration is performed during use of the second roller 41, thereby shortening the time until the reference position for forming the secondary transfer roller gap N is arranged. 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.

[0113] Furthermore, in the present embodiment, the roller bracket 47 and the first switching cam 50 and the second switching cam 51 can be driven by one roller switching motor 55. Thus, compared with the case where the roller bracket 47 and the first switching cam 50 and the second switching cam 51 are driven by different motors, the driving mechanism and the driving control can be simplified, which contributes to the cost reduction and compactness of the image forming apparatus 100.

[0114] 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 shapes and sizes of the first roller 40, the second roller 41, the roller bracket 47, the first switching cam 50, the second switching cam 51, 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.

[0115] In the above embodiment, the first position detection sensor S1 and the second position detection sensor S2 are used to limit the rotation angle of the first switching cam 50 and the second switching cam 51 and detect the arrangement and separation state of the first roller 40 and the second roller 41. However, for example, Fig.21 As shown, in addition to the second position detection sensor S2, the third position detection sensor S3 is provided in the unit frame 9a, and the third light shielding plate 47e is provided in the roller bracket 47. According to this configuration, the third light shielding plate 47e shields (turns on) the detection portion of the third position detection sensor S3 as the roller bracket 47 rotates, so that the reference position of the second roller 41 can be easily detected.

[0116] 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.

[0117] 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 onto a recording medium. By utilizing the present invention, it is possible to provide a transfer unit capable of switching two transfer rollers having different axial lengths with a simple structure, and capable of suppressing a decrease in image forming efficiency associated with switching of the transfer rollers, 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 first switching cam has a first guide hole for engaging with a first engaging portion formed on the first bearing member; A second switching cam has a second guide hole for engaging with a second engaging portion formed on the second bearing member; and a driving mechanism for rotating the roller bracket, the first switching cam and the second switching cam, By rotating the roller holder, one of the first roller and the second roller is arranged to face the image carrier, and The engaging position of the first engaging portion in the first guide hole and the engaging position of the second engaging portion in the second guide hole are changed by rotating the first switching cam and the second switching cam, and the first roller or the second roller arranged opposite to the image carrier is selectively arranged at a reference position at which the transfer roller gap is formed by being pressed against the image carrier and at a separation position at which the transfer roller is separated from the image carrier.

2. The transfer unit according to claim 1, characterized in that: The first switching cam and the second switching cam are respectively formed with recessed portions at peripheral edges of radially outer sides of the first guide hole and the second guide hole. By engaging the first engaging portion or the second engaging portion with the recessed portion, the first roller or the second roller disposed to face the image carrier is disposed at the reference position.

3. The transfer unit according to claim 2, characterized in that: The concave portions each have a bottom portion recessed to the outermost side in the radial direction and an inclined portion inclined from the bottom portion toward the inner side in the radial direction. By engaging the first engaging portion or the second engaging portion with the inclined portion, 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 separating the first engaging portion or the second engaging portion from the recessed portion, 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.

4. The transfer unit according to claim 3, characterized in that: When the toner image is not transferred to the recording medium, the first roller or the second roller arranged at the reference position is placed in the first separated state.

5. The transfer unit according to claim 3, characterized in that: When the first roller disposed opposite to the image carrier is switched to the second roller, the first roller is set to the second separated state, and when the second roller disposed opposite to the image carrier is switched to the first roller, the second roller is set to the second separated state.

6. The transfer unit according to any one of claims 1 to 5, characterized in that: The driving mechanism comprises: A shaft fixed to the rotation center of the first switching cam and the second switching cam; and The roller switching motor causes the shaft to rotate, The roller holder is rotatably supported by the shaft, and the first switching cam, the second switching cam, and the roller holder are rotated by rotating the shaft using the roller switching motor.

7. The transfer unit according to any one of claims 1 to 5, characterized in that: The transfer unit comprises: a plurality of position detection sensors for detecting positions of the roller bracket, the first switching cam, and the second switching cam in a 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.

8. An image forming device, characterized in that: include: A plurality of image forming units for forming toner images of different colors; An endless intermediate transfer belt as an 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 As the secondary transfer unit of any one of claims 1 to 7, the toner image primarily transferred onto the intermediate transfer belt is secondarily transferred onto a recording medium.

Images