Image forming apparatus

Abstract

To provide an image forming apparatus having a support member that supports an arm member and is formed of metal so as to prevent the insulation deterioration of a resin member around a member for power supply for supplying power to the support member and a transfer roller.SOLUTION: An image forming apparatus 100 has a pressure spring 400 that applies pressure to a transfer roller 41, an application unit 34 that applies voltage to the transfer roller 41 through the pressure spring 400, and a support member 406 that supports an arm member 407 and is formed of metal. A spring seating face 417 is located between the support member 406 and the pressure spring 400, and is provided with a rib shape 415 extending in a pressure direction of the pressure spring 400.SELECTED DRAWING: Figure 13

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile apparatus, or a multifunction machine having a plurality of functions among these, using an electrophotographic method or an electrostatic recording method.

Background Art

[0002] Conventionally, as an image forming apparatus such as a copying machine using an electrophotographic method, there is one that employs an intermediate transfer method. This image forming apparatus forms an image on a recording material by primarily transferring a toner image formed on a photoreceptor onto an intermediate transfer member and secondarily transferring the toner image on the intermediate transfer member onto the recording material such as paper. As the intermediate transfer member, an intermediate transfer belt stretched over a plurality of tension rollers is often used. The secondary transfer is often performed by applying a secondary transfer voltage to a secondary transfer roller (transfer roller) that contacts one of the plurality of tension rollers, which is a secondary transfer opposing roller, via the intermediate transfer belt.

[0003] The secondary transfer roller is pressed against the secondary transfer opposing roller via the intermediate transfer belt with a predetermined contact pressure to form a nip portion (secondary transfer nip portion) between the intermediate transfer belt. In such a configuration, if the state where the contact pressure is applied to the secondary transfer roller continues, deformation (contact trace) occurs on the surface of the secondary transfer roller, making appropriate secondary transfer difficult and potentially deteriorating the print image quality. Therefore, the image forming apparatus may be provided with a contact separation mechanism that separates and contacts the secondary transfer roller with respect to the intermediate transfer belt, and may be configured such that the secondary transfer roller is separated from the intermediate transfer belt when the printing operation is not performed.

[0004] In Patent Document 1, a configuration is proposed in which a bearing member (arm) that supports the secondary transfer roller and an eccentric cam that moves the bearing member are used to separate the secondary transfer roller from the intermediate transfer belt. However, in this configuration, when it is desired to increase the separation amount, an increase in the size of the eccentric cam and, accordingly, an increase in the size of the image forming apparatus become problems.

[0005] In Patent Document 2, a configuration is proposed in which a bearing member (first arm member) that supports a secondary transfer roller, an arm member (second arm member) connected thereto, and an eccentric cam that moves the bearing member (first arm member) via the arm member (second arm member) are used to separate the secondary transfer roller from the intermediate transfer belt. In Patent Document 2, it is said that the above configuration can suppress the enlargement of the configuration for separating the secondary transfer roller from the intermediate transfer belt.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In a configuration in which a bearing member of a secondary transfer roller is moved using an arm member, for example, when separating the secondary transfer roller from the intermediate transfer belt, a reaction force due to a biasing member that biases the secondary transfer roller acts on the arm member. Therefore, a high strength and rigidity are required for the support member that supports the arm member. If the strength and rigidity of the support member are insufficient, there is a possibility that the product life may be reduced due to damage to the support member, or the intended separation distance may be reduced due to deformation of the support member.

[0008] Therefore, it is conceivable to use a member formed of a metal such as sheet metal as the support member that supports the arm member. However, since a secondary transfer voltage is applied to the secondary transfer roller, when the support member is formed of a metal that is a conductor, insulation deterioration of the resin member around the power supply member for supplying power to the support member and the secondary transfer roller may occur.

[0009] Therefore, an object of the present invention is to suppress insulation deterioration of a resin member around a power supply member for supplying power to a support member and a transfer roller in a configuration where the support member supporting the arm member is formed of metal.

Means for Solving the Problems

[0010] The above object is achieved by an image forming apparatus according to the present invention. Briefly, the present invention includes an image carrier that carries a toner image, an intermediate transfer belt that is stretched around a plurality of stretching rollers and to which the toner image is transferred from the image carrier, a transfer roller that can be in contact with the outer peripheral surface of the intermediate transfer belt and forms a transfer nip portion where the toner image is transferred from the intermediate transfer belt to a recording material in cooperation with an opposing roller among the plurality of stretching rollers, a bearing member made of an electrically insulating resin that supports an end portion of the transfer roller in the rotational axis direction, a pressurizing spring that pressurizes the bearing member so as to pressurize the transfer roller against the intermediate transfer belt, a holding member that holds the bearing member so as to be movable between a first position where the transfer roller contacts the intermediate transfer belt and a second position where the transfer roller is separated from the intermediate transfer belt along the pressurizing direction of the pressurizing spring, an arm member that can engage with the bearing member and moves the bearing member from the first position to the second position against the pressurizing force of the pressurizing spring, a support member made of metal that rotatably supports the arm member, an applying portion that applies a voltage to the transfer roller through the pressurizing spring, and a connecting member that electrically connects the pressurizing spring and the transfer roller. The pressurizing spring is disposed between a receiving portion provided on the bearing member and a spring support portion provided on the holding member. When viewed along the pressurizing direction of the pressurizing spring, the closest portion of the support member to the pressurizing spring is disposed adjacent to a spring seat surface that is a surface provided with the spring support portion of the holding member. The holding member has a rib-shaped portion that extends along the pressurizing direction of the pressurizing spring from the spring seat surface between the pressurizing spring and the support member on a straight line passing through the closest portion of the support member to the pressurizing spring and the closest portion of the pressurizing spring to the support member when viewed along the pressurizing direction of the pressurizing spring. The image forming apparatus is characterized by this.

Advantages of the Invention

[0011] According to the present invention, in a configuration where a support member that supports an arm member is formed of metal, it is possible to suppress insulation deterioration of a resin member around a power supply member for supplying power to the support member and the transfer roller.

Brief Description of the Drawings

[0012]

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Mode for Carrying Out the Invention

[0013] Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[0014] [Example 1] 1. Overall Configuration and Operation of the Image Forming Apparatus FIG. 1 is a schematic cross-sectional view of the image forming apparatus 100 of the present embodiment (showing a cross-section substantially orthogonal to the rotation axis direction of the photosensitive drum 1 described later). The image forming apparatus 100 of the present embodiment is a tandem type multifunction machine (having functions of a copying machine, a printer, and a facsimile apparatus) adopting an intermediate transfer method. The image forming apparatus 100 can form a full-color image on a sheet-like recording material (transfer material, sheet material, recording medium, medium) P such as paper by using an electrophotographic method according to an image signal (image information) transmitted from an external device such as a personal computer.

[0015] Here, with respect to the image forming apparatus 100 and its elements, the front side of the paper surface in FIG. 1 is defined as the "front (front) side", and the back side of the paper surface is defined as the "rear (back) side". The front-rear direction connecting the front side and the rear side is substantially parallel to the rotation axis direction of the photosensitive drum 1, the tension rollers 22 to 25 of the intermediate transfer belt 21, or the secondary transfer roller 41 described later. Also, with respect to the image forming apparatus 100 and its elements, the up-down direction refers to the up-down direction in the gravitational direction (vertical direction), but it does not mean only directly above and directly below, but includes the upper side and the lower side with respect to the horizontal plane passing through the element or position of interest.

[0016] The image forming apparatus 100 includes four image forming units 10Y, 10M, 10C, and 10K that form images of yellow (Y), magenta (M), cyan (C), and black (K) respectively as a plurality of image forming units (stations). These image forming units 10Y, 10M, 10C, and 10K are arranged in series along the moving direction of the image transfer surface disposed substantially horizontally of the intermediate transfer belt 21 described later. Note that, for elements having the same or corresponding functions or configurations provided for each color, the Y, M, C, and K at the end of the reference numerals indicating that they are elements for any one of the colors may be omitted and they may be collectively described. FIG. 2 is a schematic cross-sectional view showing one representative image forming unit 10. In the present embodiment, the image forming unit 10 includes a photosensitive drum 1 (1Y, 1M, 1C, 1K) which is a rotatable drum-shaped (cylindrical) photosensitive member (electrophotographic photosensitive member) as an image carrier, a charging roller 2 (2Y, 2M, 2C, 2K), an exposure device 3 (3Y, 3M, 3C, 3K), a developing device 4 (4Y, 4M, 4C, 4K), a cleaning device 5 (5Y, 5M, 5C, 5K), a cleaning roller 6 (6Y, 6M, 6C, 6K), and the like.

[0017] The image forming unit 10 is provided with a photosensitive drum 1 which is a rotatable drum-shaped (cylindrical) photosensitive member (electrophotographic photosensitive member) as an image carrier. The photosensitive drum 1 is rotationally driven in the direction of the arrow (clockwise direction) in FIG. 1 by transmitting a driving force from a drum driving unit 51 (FIG. 3) as driving means including a drum driving motor as a driving source. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 2 which is a roller-shaped charging member as charging means. The charging roller 2 is disposed in contact with the surface of the photosensitive drum 1 and is driven to rotate passively as the photosensitive drum 1 rotates. During the charging process, a predetermined charging voltage (charging bias) is applied to the charging roller 2 by a charging power source (high voltage power source) 31 (FIG. 3) as a charging voltage applying unit.

[0018] The surface of the charged photosensitive drum 1 is exposed by an exposure device 3 as an exposure means (electrostatic image forming means), and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1. In this embodiment, the exposure device 3 irradiates the surface of the photosensitive drum 1 with light emitted by an LED as a light source in accordance with an image signal input from a control unit 120 (FIG. 3). Note that the exposure device 3 may be a laser scanner device or the like, and may be configured as a single unit that exposes, for example, four photosensitive drums 1.

[0019] The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by supplying toner by a developing device 4 as a developing means, and a toner image (toner picture, developer image) is formed on the photosensitive drum 1. In this embodiment, the developing device 4 uses a two-component developer including toner (non-magnetic toner particles) and a carrier (magnetic carrier particles) as a developer. The developing device 4 includes a developing sleeve 4a as a developer carrier and a developing container 4b that houses the developer. The developing sleeve 4a carries the developer in the developing container 4b and transports it to a developing position that is the opposing portion with the photosensitive drum 1. During development, the developing sleeve 4a is rotationally driven by transmitting a driving force from, for example, a drum driving unit 51. Also, during development, a predetermined developing voltage (developing bias) is applied to the developing sleeve 4a by a developing power source (high voltage power source) 32 (FIG. 3) as a developing voltage application unit. Thereby, the toner of the developer carried on the developing sleeve 4a is supplied onto the photosensitive drum 1 according to the electrostatic image, and a toner image is formed on the photosensitive drum 1. In this embodiment, toner charged with the same polarity (negative polarity in this embodiment) as the charging polarity of the photosensitive drum 1 adheres to the exposed portion (image portion) on the photosensitive drum 1 where the absolute value of the potential has decreased by being exposed after being uniformly charged (inversion development method). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative.

[0020] An endless rotatable belt as an intermediate transfer member, i.e., an intermediate transfer belt 21, is arranged so as to face four photosensitive drums 1Y, 1M, 1C, and 1K. The intermediate transfer belt 21 is stretched over a plurality of stretching rollers (support rollers), i.e., a driving roller 22, a tension roller 23, an upstream auxiliary roller 24, and a pre-secondary transfer roller 25, and is stretched with a predetermined tension. The driving roller 22 is rotationally driven in the direction of the arrow in FIG. 1 (counterclockwise) by transmitting a driving force from a belt driving unit 52 (FIG. 3) as driving means including a belt driving motor as a driving source. The intermediate transfer belt 21 is rotationally driven (circumferentially moved) in the direction of the arrow in FIG. 1 by inputting a driving force from the driving roller 22. The tension roller 23 applies a predetermined tension to the intermediate transfer belt 21. The upstream auxiliary roller 24 is arranged upstream of a primary transfer nip portion N1 described later in the rotational direction (surface movement direction, conveyance direction) of the intermediate transfer belt 21, and forms an image transfer surface that is arranged substantially horizontally together with the pre-secondary transfer roller 25. The pre-secondary transfer roller 25 forms the surface of the intermediate transfer belt 21 in the vicinity upstream of a secondary transfer nip portion N2 described later in the rotational direction of the intermediate transfer belt 21. The driving roller 22 also serves as a secondary transfer counter roller (secondary transfer inner roller) as a counter member (counter electrode) of a secondary transfer roller 41 described later. On the inner peripheral surface side of the intermediate transfer belt 21, roller-shaped primary transfer members as primary transfer means, i.e., primary transfer rollers 26Y, 26M, 26C, and 26K, are respectively arranged corresponding to the photosensitive drums 1Y, 1M, 1C, and 1K. The primary transfer roller 26 is pressed toward the photosensitive drum 1, abuts on the photosensitive drum 1 via the intermediate transfer belt 21, and forms a primary transfer nip portion (primary transfer portion) N1 (N1Y, N1M, N1C, N1K), which is a contact portion between the photosensitive drum 1 and the intermediate transfer belt 21. The stretching rollers other than the driving roller 22 and each primary transfer roller 26 are rotationally driven in a driven manner as the intermediate transfer belt 21 rotates.

[0021] The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the rotating intermediate transfer belt 21 as the transfer medium at the primary transfer nip N1 by the action of the primary transfer roller 26. At the time of primary transfer, a primary transfer voltage (primary transfer bias), which is a DC voltage of the opposite polarity to the normal charging polarity of the toner (positive polarity in this embodiment), is applied to the primary transfer roller 26 by a primary transfer power source (high-voltage power source) 33 (Fig. 3) serving as a primary transfer voltage application unit. For example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black formed on each photosensitive drum 1 are sequentially transferred so as to be superimposed on the same image formation area on the intermediate transfer belt 21.

[0022] On the outer peripheral surface side of the intermediate transfer belt 21, at a position facing the driving roller 22, a secondary transfer roller (secondary transfer outer roller) 41, which is a roller-shaped secondary transfer member (transfer rotating body) as secondary transfer means, is disposed. The secondary transfer roller 41 is pressurized toward the driving roller 22 via the intermediate transfer belt 21 under the pressure of a pressurizing spring 400 constituted by a compression coil spring as an urging member (elastic member, pressurizing member) serving as an urging means. Thereby, the secondary transfer roller 41 forms a secondary transfer nip portion (secondary transfer portion) N2, which is a contact portion between the intermediate transfer belt 21 and the secondary transfer roller 41. In this embodiment, the secondary transfer roller 41 rotates in a driven manner as the intermediate transfer belt 21 rotates. Note that the secondary transfer roller 41 may be configured to rotate in a driving manner. The toner image formed on the intermediate transfer belt 21 is transferred (secondary transfer) onto a recording material P as the transfer medium sandwiched between the intermediate transfer belt 21 and the secondary transfer roller 41 and conveyed at the secondary transfer nip portion N2 by the action of the secondary transfer roller 41. At the time of secondary transfer, a secondary transfer voltage (secondary transfer bias), which is a DC voltage of the opposite polarity to the normal charging polarity of the toner (positive polarity in this embodiment), is applied to the secondary transfer roller 41 by a secondary transfer power source (high-voltage power source) 34 (Fig. 3) serving as a secondary transfer voltage application unit. The secondary transfer voltage is, for example, about 1 to 3 kV. Note that the driving roller (secondary transfer opposing roller) 22 is electrically grounded (connected to the ground).

[0023] The recording material P is stored in a cassette (recording material storage) 11 as a feeding unit. The recording material P is fed out one by one from the cassette 11 by a feeding roller 18 or the like as a feeding member. The recording material P is conveyed by a pair of pre-registration rollers 14 that are rotationally driven by a pre-registration roller driving unit (not shown) and is conveyed to the resist adjustment unit 12. After the posture of the recording material P is adjusted in the resist adjustment unit 12, it is conveyed to the secondary transfer nip portion N2 at a predetermined timing with respect to the toner image on the intermediate transfer belt 21. The resist adjustment unit 12 includes a pair of resist rollers (resist roller pair) 13 that are roller-shaped conveying members as conveying means, and a resist roller driving unit (not shown) as driving means for driving the resist roller pair 13. When the resist roller pair 13 is rotationally driven by the resist roller driving unit, the recording material P is conveyed at the contact portion (nip portion) formed between the rollers of the resist roller pair 13. Note that the resist roller driving unit drives at least one (both may be) of the resist roller pair 13.

[0024] The recording material P onto which the toner image has been transferred is conveyed to a fixing device 15 as a fixing means. The fixing device 15 fixes (melts and adheres) the toner image to the surface of the recording material P by heating and pressing the recording material P carrying the unfixed toner image. The recording material P onto which the toner image has been fixed is discharged (output) to a discharge tray 17 as a discharge unit provided outside (outside the machine) of the apparatus main body (hereinafter, also simply referred to as the "apparatus main body") 110 of the image forming apparatus 100 by a discharge roller 16 or the like as a discharge member.

[0025] On one hand, the toner remaining on the photosensitive drum 1 after the first transfer (the toner remaining after the first transfer) is removed from the photosensitive drum 1 by a cleaning device 5 as a cleaning means and recovered. The cleaning device 5 scrapes the toner remaining after the first transfer from the surface of the rotating photosensitive drum 1 by a cleaning blade 5a as a cleaning member disposed in contact with the surface of the photosensitive drum 1, and accommodates it in a cleaning container 5b. Further, on the outer peripheral surface side of the intermediate transfer belt 21, a belt cleaning device 28 as an intermediate transfer body cleaning means is disposed at a position facing the tension roller 23 via the intermediate transfer belt 21. Toner remaining on the intermediate transfer belt 21 after the second transfer (toner remaining after the second transfer) and deposits such as paper powder attached to the intermediate transfer belt 21 from the recording material P are removed from the intermediate transfer belt 21 by the belt cleaning device 28 and recovered. Further, the surface of the charging roller 2 is cleaned by a cleaning roller 6 which is a rotatable roller-shaped cleaning member as a charging member cleaning means disposed in contact with the surface of the charging roller 2.

[0026] In this embodiment, in each image forming unit 10, the photosensitive drum 1, the charging roller 2, the cleaning device 5, and the cleaning roller 6 constitute a drum cartridge that is integrally detachable from the apparatus main body 110. Further, in this embodiment, in each image forming unit 10, the developing device (developing unit) 4 constitutes a developing cartridge that is substantially independently detachable from the apparatus main body 110.

[0027] Further, in this embodiment, the intermediate transfer belt 21, each tension roller 22 to 25, each first transfer roller 26, the belt cleaning device 28, and a frame (not shown) supporting them constitute an intermediate transfer unit 20 as a belt conveyance device. The intermediate transfer unit 20 is integrally detachable from the apparatus main body 110 for maintenance or replacement work.

[0028] 2. Control Configuration FIG. 3 is a schematic block diagram showing the control configuration of the image forming apparatus 100 of the present embodiment. The image forming apparatus 100 is provided with a control unit (control circuit) 120 as control means. The control unit 120 includes a CPU 121 as arithmetic processing means, a memory 121 including a ROM, a RAM, etc. as storage means, and an input / output unit (not shown) for inputting and outputting signals to and from the control unit 120. Programs and table data for controlling each part of the image forming apparatus 100 are stored in the ROM. Data related to control is temporarily stored in the RAM. The CPU 121 controls each part of the image forming apparatus 100 according to the programs stored in the ROM and executes an image forming operation and the like.

[0029] Various power supplies such as a charging power supply 31, a developing power supply 32, a primary transfer power supply 33, and a secondary transfer power supply 34 are connected to the control unit 120, and these various power supplies are controlled by signals from the control unit 120. Although not shown in the figure, in the present embodiment, the charging power supply 31, the developing power supply 32, and the primary transfer power supply 33 are provided independently for each image forming unit 10. Further, an exposure device 3 is connected to the control unit 120, and the exposure device 3 is controlled by a signal from the control unit 120. In the present embodiment, the exposure device 3 is provided independently for each image forming unit 10. Further, various drive units such as a drum drive unit 51, a belt drive unit 52, and an abutment separation drive unit 53 for driving an abutment separation mechanism 425 (FIGS. 9 and 10) described later are connected to the control unit 120, and these various drive units are controlled by signals from the control unit 120.

[0030] 3. Right Door Unit As shown in FIG. 4, the image forming apparatus 100 has a right door unit 130 as an opening / closing member for opening the inside of the apparatus main body 110 on the right side portion when the apparatus main body 110 is viewed from the front side. The right door unit 130 is configured to rotate the upper part downward (in the direction of arrow D in FIG. 4) around a rotation axis 131 provided below and substantially parallel to the front-rear direction to open, and rotate the upper part upward (in the direction of arrow D' in FIG. 5 (opposite to the direction of arrow D)) to close.

[0031] The right door unit 130 is opened and closed by operating a handle provided on the right door unit 130 by an operator such as a user or a service person. The right door unit 130 opens at least a part of the conveyance path of the recording material P from the cassette 11 through the secondary transfer nip portion N2 to the fixing device 15 so as to divide the front side (the side where the toner image is transferred) and the back side of the recording material P. The secondary transfer roller 41 is provided in a secondary transfer unit 40 described later, which is attached to the right door unit 130. When the right door unit 130 is opened, the right door unit 130 is opened in such a manner that the secondary transfer roller 41 is separated from the intermediate transfer belt 21.

[0032] By opening the right door unit 130, the operator can access the intermediate transfer unit 20 mounted in the apparatus main body 110, the secondary transfer roller 41 provided in the secondary transfer unit 40 attached to the right door unit 130, and the like. Thereby, the operator can attach and detach the intermediate transfer unit 20 to and from the apparatus main body 110, replace and clean the secondary transfer roller 41, and the like.

[0033] 4. Overall Configuration of Secondary Transfer Unit Next, the overall configuration of the secondary transfer unit 40 in the present embodiment will be described.

[0034] Here, for the intermediate transfer unit 40 and its elements, the rotational axis direction of the secondary transfer roller 41 is defined as the Y direction (the direction from the front side to the rear side is the positive direction). Also, for the intermediate transfer unit 40 and its elements, the moving direction of the secondary transfer roller 41 and a bearing member 402 described later when the secondary transfer roller 41 is brought into contact with or separated from the intermediate transfer belt 21 is defined as the Z direction (the moving direction when separating is the positive direction). This Z direction is substantially parallel to the pressurizing direction of a pressurizing spring 400 described later (the expansion and contraction direction of the pressurizing spring 400) (the direction opposite to the pressurizing direction is the positive direction). Further, the direction orthogonal to the Y direction and the Z direction is defined as the X direction (the direction from the upstream side to the downstream side in the conveyance direction of the recording material P is the positive direction).

[0035] FIG. 5 is an external perspective view of the secondary transfer unit 40 in this embodiment. In FIG. 5, the rear side is shown on the left side of the drawing sheet, and the front side is shown on the right side of the drawing sheet.

[0036] The secondary transfer unit 40 includes a secondary transfer roller 41, bearing members 402 that support the secondary transfer roller 41 at both ends in the axial direction of the secondary transfer roller 41, a holder 404 that holds the bearing members 402, and the like.

[0037] The secondary transfer roller 41 has a roller portion 41a formed of an elastic body that constitutes an elastic layer (a foamed elastic layer in this embodiment), and a shaft portion 41b that constitutes a core metal portion. In this embodiment, the roller portion 41a is composed of a sponge (foamed elastic body) formed of NBR rubber or EPDM rubber containing a conductive agent such as a metal complex or carbon. Also, in this embodiment, the shaft portion 41b is made of metal. At both ends in the axial direction of the secondary transfer roller 41, the shaft portion 41b protrudes from the roller portion 41a. Also, a pair of bearings 401 are attached to the shaft portions 41b at both ends. In this embodiment, ball bearings are used as the bearings 401. The bearings 401 have sufficient conductivity to connect the secondary transfer roller 41 to a power supply path (current-carrying path). In this embodiment, the outer ring, inner ring, and balls of the bearings 401 are each made of metal.

[0038] The holder 404 has bearing member holding portions 441 that slidably hold the bearing members 402 at both ends in the axial direction of the secondary transfer roller 41. A roller accommodating portion 442 for accommodating the secondary transfer roller 41 is formed between the bearing member holding portions 441 at both ends. Also, the holder 404 has a first recording material guide portion 443 that guides the recording material P conveyed from the upstream side toward the secondary transfer nip portion N2, and a second recording material guide portion 444 that guides the recording material P conveyed from the secondary transfer nip portion N2 to the downstream side. The secondary transfer roller 41 is supported via the bearings 401 by the bearing members 402 movably held by the holder 404 at both ends in its axial direction.

[0039] 5. Pressurization and Power Supply Structure Next, the pressurization and power supply structure of the secondary transfer roller 41 in this embodiment will be described.

[0040] FIG. 6 is a schematic perspective view of the rear bearing member 402 (the pressurizing spring 400 is also shown). FIGS. 7 and 8 are schematic cross-sectional views in the vicinity of the bearing member 402 showing the pressurization and power supply structure of the rear end portion in the rotational axis direction of the secondary transfer roller 41, respectively. FIG. 7 shows a cross-section substantially orthogonal to the rotational axis direction of the secondary transfer roller 41, and FIG. 8 shows a cross-section along the rotational axis direction of the secondary transfer roller 41.

[0041] In this embodiment, the pressurization of the secondary transfer roller 41 is performed in the same manner at both end portions in the rotational axis direction of the secondary transfer roller 41. On the other hand, in this embodiment, the power supply to the secondary transfer roller 41 is performed at the rear end portion, which is one end portion in the rotational axis direction of the secondary transfer roller 41. Therefore, mainly, the pressurization and power supply structure of the rear end portion in the rotational axis direction of the secondary transfer roller 41 will be described here. However, the structure described below may be replaced with the front end portion in the rotational axis direction of the secondary transfer roller 41.

[0042] First, the pressurization structure of the secondary transfer roller 41 will be described. The secondary transfer roller 41 is rotatably supported by a bearing 401. Further, the bearing 401 is supported by a bearing member 402. Furthermore, the bearing member 402 that supports the secondary transfer roller 41 via the bearing 401 is held by a holder 404 so as to be movable along the pressurization direction of the pressurizing spring 500 (arrow F direction (or -Z direction) in the figure). The bearing member 402 and the holder 404 are each made of an electrically insulating resin.

[0043] The bearing member 402 is provided with a roller mounting portion 423 (Fig. 6), and a bearing 401 attached to the shaft portion 41b of the secondary transfer roller 41 is disposed on the roller mounting portion 423. The roller mounting portion 423 is open upward (-Z direction in Fig. 6) so as to be able to receive the bearing 401. The bearing member 402 has a first roller support surface 421 as a roller support portion that can contact the outer peripheral surface of the bearing 401 so as to be exposed to the roller mounting portion 423. The holder 404 has a spring seat surface 417 provided with a spring support portion 405 that supports one end portion of the pressure spring 400 in the expansion and contraction direction. The other end portion of the pressure spring 400 in the expansion and contraction direction is brought into contact with a first receiving portion (pressure receiving portion) 422 provided on the bearing member 402. That is, the pressure spring 400 is disposed between the first receiving portion 422 of the bearing member 402 and the spring seat surface 417 (spring support portion 405) of the holder 404. Therefore, the secondary transfer roller 41 is pressed toward the intermediate transfer belt 21 (secondary transfer counter roller 22) by receiving the pressing force from the pressure spring 400 via the bearing member 402 and the bearing 401. The pressure spring 400 is composed of a compression coil spring formed of a conductive metal.

[0044] Next, the power supply configuration for the secondary transfer roller 41 will be described. As described above, during secondary transfer, a secondary transfer voltage is applied to the secondary transfer roller 41 by the secondary transfer power supply 34 (FIG. 3) provided in the image forming apparatus 100. In this embodiment, a power supply chip 500 as a connection member that electrically connects the pressure spring 400 and the secondary transfer roller 41 is held by the bearing member 402. The power supply chip 500 has a second roller support surface 501 as a roller support portion that can contact the outer peripheral surface of the bearing 401 so as to be exposed to the above-described roller mounting portion 423 of the bearing member 402. The second roller support surface 501 of the power supply chip 500 is disposed adjacent to the above-described first roller support surface 421 of the bearing member 402. Further, the power supply chip 500 has a second receiving portion (pressure receiving portion) 502 against which the pressure spring 400 abuts. The end portion on the side where the above-described first receiving portion 422 of the bearing member 402 in the expansion and contraction direction of the pressure spring 400 is brought into contact is also brought into contact with the second receiving portion 502 of the power supply chip 500. That is, the pressure spring 400 is disposed between the first receiving portion 422 of the bearing member 402 and the spring seat surface 417 (spring support portion 405) of the holder 404 as described above, and between the second receiving portion 502 of the power supply chip 500 and the spring seat surface 417 (spring support portion 405) of the holder 404. Therefore, the power supply chip 500 is pressurized by the pressure spring 400 that pressurizes the bearing member 402 and pressed against the bearing 401. Thus, in this embodiment, the pressure spring 400 contacts the bearing member 402 and pressurizes it toward the bearing 401, and contacts the power supply chip 500 and pressurizes it toward the bearing 401. The power supply chip 500 is made of a conductive material, particularly, in this embodiment, a conductive resin (conductive resin). Note that the power supply chip 500 may be formed of another conductive material such as metal.

[0045] Furthermore, a power supply spring 403 as a power supply member for supplying power from the secondary transfer power supply 34 to the pressure spring 400 is attached to the holder 404. The power supply spring 403 is composed of a wire spring formed of a conductive metal. One end side of the wire material constituting the power supply spring 403 is extended within the holder 404 and brought into contact with the pressure spring 400. A part of this end side of the power supply spring 403 is disposed on the spring seat surface 417. Also, the power supply spring 403 is electrically connected to the secondary transfer power supply 34 via the other end side of the wire material constituting it and the power supply path outside the holder 404. In this embodiment, the pressure spring 400, the power supply spring 403, and the power supply chip 500 constitute a power supply member for supplying power to the secondary transfer roller 41 in the secondary transfer unit 40.

[0046] A voltage is applied to the power supply spring 403 from the secondary transfer power supply 34 via the power supply path outside the holder 404. And the power supply spring 403 is electrically connected to the pressure spring 400, the power supply chip 500, the bearing 401, and the secondary transfer roller 41 (shaft portion 41b, roller portion 41a). Thereby, the power supply path (energization path) from the secondary transfer power supply 34 to the secondary transfer roller 41 is connected, and a secondary transfer voltage can be applied to the secondary transfer roller 41.

[0047] Note that the front bearing member 402 in the rotational axis direction of the secondary transfer roller 41 has the same configuration as the above-described rear bearing member 402 (substantially symmetric with respect to a plane passing through the center in the rotational axis direction of the secondary transfer roller 41 and substantially orthogonal to the rotational axis direction of the secondary transfer roller 41). However, as described above, power supply to the secondary transfer roller 41 is performed at the front end in the rotational axis direction of the secondary transfer roller 41. Therefore, the front bearing member 402 is not provided with the power supply chip 500 and is integrally formed of an electrically insulating resin as a whole.

[0048] 6. Contact and separation configuration of the secondary transfer roller Next, the contact and separation configuration of the secondary transfer roller 41 in this embodiment will be described.

[0049] Here, the contact / separation configuration at the rear end in the rotational axis direction of the secondary transfer roller 41 will be described. However, the contact / separation configuration at the front end in the rotational axis direction of the secondary transfer roller 41 is the same (substantially symmetric with respect to a plane passing through the center in the rotational axis direction of the secondary transfer roller 41 and substantially orthogonal to the rotational axis direction of the secondary transfer roller 41).

[0050] Figs. 9 and 10 are schematic cross-sectional views in the vicinity of the bearing member 402 showing the contact / separation configuration of the rear end in the rotational axis direction of the secondary transfer roller 41. Fig. 9 shows a state where the secondary transfer roller 41 is in contact with the intermediate transfer belt 21 (secondary transfer opposing roller 22), and Fig. 10 shows a state where the secondary transfer roller 41 is separated from the intermediate transfer belt 21 (secondary transfer opposing roller 22).

[0051] As described above, the secondary transfer roller 41 is supported by the bearing member 402 so as to be movable along the pressing direction (-Z direction) of the pressing spring 400. During secondary transfer (during image formation), the secondary transfer roller 41 is pressed toward the intermediate transfer belt 21 with a predetermined pressing force (contact pressure). Here, if the state where the contact pressure is applied to the secondary transfer roller 41 continues, deformation (contact trace) occurs on the surface of the secondary transfer roller 41, making appropriate secondary transfer difficult and potentially degrading the print image quality. Therefore, in this embodiment, the secondary transfer unit 40 is provided with a contact separation mechanism 425 that contacts and separates the secondary transfer roller 41 from the intermediate transfer belt 21. When the printing operation is not performed, the secondary transfer roller 41 is separated from the intermediate transfer belt 21. Specifically, for example, in the standby state where the power of the image forming apparatus 100 is ON and the image forming apparatus 100 is waiting for print information (including an instruction to start the printing operation) to be input, the secondary transfer roller 41 is in a state separated from the intermediate transfer belt 21. Then, when print information is input to the image forming apparatus 100 and the printing operation is performed, the secondary transfer roller 41 is brought into contact with the intermediate transfer belt 21 at a predetermined timing, and when the printing operation ends, the secondary transfer roller 41 is separated from the intermediate transfer belt 21. Also, for example, when the power of the image forming apparatus 100 is turned OFF, the secondary transfer roller 41 is separated from the intermediate transfer belt 21, and this state is maintained when the power of the image forming apparatus 100 is OFF.

[0052] As shown in FIGS. 9 and 10, in this embodiment, the contact separation mechanism 425 is configured to include a support plate 406, an arm member 407, an arm shaft 408, a cam 409, a cam shaft 410, and the like. The support plate 406 as a support member is attached to the holder 404 adjacent to the bearing member 402 in the rotational axis direction of the secondary transfer roller 41. An arm shaft 408 that rotatably (rockably) supports the arm member 407 is fixed to the support plate 406. The arm shaft 408 is provided on the support plate 406 so as to protrude from the end side toward the center side in the rotational axis direction of the secondary transfer roller 41 along the rotational axis direction of the secondary transfer roller 41 (substantially parallel in this embodiment). And the arm member 407 is rotatably attached to this arm shaft 408. Further, the support plate 406 rotatably supports a cam shaft 410 to which a cam 409 is fixed. The cam shaft 410 extends along the rotational axis direction of the secondary transfer roller 41 (substantially parallel in this embodiment). In this embodiment, one cam shaft 410 is supported by support plates 406 provided at both ends in the rotational axis direction of the secondary transfer roller 41, respectively. And a cam (eccentric cam) 409 is fixed to this cam shaft 410. A drive transmission part such as a gear is fixed to the cam shaft 410, and the driving force from the contact separation drive part 53 (FIG. 3) provided in the image forming apparatus 100 is transmitted to the cam shaft 410 via this drive transmission part. Thereby, the cam 409 can be rotated around the cam shaft 410. The contact separation drive part 53 operates under the control of the control part 120.

[0053] Note that the arm shaft 408 may be composed of a single shaft member supported by the support plates 406 at both ends in the rotational axis direction of the secondary transfer roller 41, similar to the cam shaft 410 in this embodiment. Further, the cam shaft 410 may be composed of shaft members respectively provided on the support plates 406 at both ends in the rotational axis direction of the secondary transfer roller 41, similar to the arm shaft 408 in this embodiment.

[0054] The arm member 407 has a first arm portion 471 that can engage with a depression surface 411 as an engaged portion provided on the bearing member 402, and a second arm portion 472 that can engage with the cam 409. The first arm portion 471 and the second arm portion 472 extend on opposite sides with a support receiving portion 473 rotatably supported by an arm shaft 408 therebetween. As shown in FIG. 8, the depression surface 411 of the bearing member 402 is provided so as to protrude toward the central side in the central side of the secondary transfer roller 41 rather than the spring seat surface 417 of the holder 404 in the rotational axis direction of the secondary transfer roller 41. As shown in FIG. 8, the bearing member 402 is continuously provided from the end portion on the first roller support surface 421 side in the pressing direction (-Z direction) of the pressing spring 400 to at least the depression surface 411 provided on the side opposite to the first roller support surface 421 rather than the spring seat surface 417 of the holder 404. Further, as shown in FIG. 8, the support plate 406 is disposed between the depression surface 411 of the bearing member 402 and the spring seat surface 417 of the holder 404 in the rotational axis direction of the secondary transfer roller 41.

[0055] As shown in FIG. 9, by rotating the cam 409 in the direction of arrow A (counterclockwise direction) in FIG. 9, the cam 409 abuts against the second arm portion 472 of the arm member 407, and rotates the arm member 407 in the direction of arrow B (clockwise direction) in FIG. 9. When the arm member 407 rotates in the direction of arrow B in FIG. 9 in this way, the first arm portion 471 of the arm member 407 abuts against the depression surface 411. By further continuing to rotate the arm member 407 in the direction of arrow B in FIG. 9, the bearing member 402 moves in the direction opposite to the pressing direction of the pressing spring 400 (Z direction) against the pressing force of the pressing spring 400. Then, as shown in FIG. 10, the secondary transfer roller 41 is in a state of being separated from the intermediate transfer belt 21.

[0056] Also, as shown in FIG. 10, by rotating the cam 409 in the direction of arrow A' (clockwise direction) in FIG. 10, the cam 409 is separated from the second arm portion 472 of the arm member 407. Accordingly, the bearing member 402 moves in the pressurizing direction (-Z direction) of the pressurizing spring 400 by the pressurizing force of the pressurizing spring 400. Then, as shown in FIG. 9, the secondary transfer roller 41 comes into contact with the intermediate transfer belt 21. At this time, the arm member 407 rotates in the direction of arrow B' (counterclockwise direction) in FIG. 10, and the first arm portion 471 of the arm member 407 is separated from the pressing surface 411. In the present embodiment, the arm member 407 is configured to rotate in the direction of arrow B' in FIG. 10 by the action of gravity until the first arm portion 471 is separated from the pressing surface 411 after the secondary transfer roller 41 comes into contact with the intermediate transfer belt 21.

[0057] Note that the cams 409 at both ends in the rotational axis direction of the secondary transfer roller 41 operate in synchronization with each other by the rotation of the cam shaft 410 to bring the secondary transfer roller 41 into contact with and separate from the intermediate transfer belt 21.

[0058] Here, in the present embodiment, the support plate 406 receives the reaction force from the pressurizing spring 400 from the cam shaft 410 and the arm shaft 408 in a state where the secondary transfer roller 41 is separated from the intermediate transfer belt 21. Therefore, in the present embodiment, in order to prevent deformation and breakage of the support plate 406 due to this reaction force, the support plate 406 is formed of a member made of metal, specifically, a sheet metal made of SUS (stainless steel), which is a conductive metal. Note that the arm member 407 and the cam 409 are made of an electrically insulating resin, and the arm shaft 408 and the cam shaft 410 are made of a conductive metal. Also, in the present embodiment, the support plate 406 is electrically grounded.

[0059] 7. Shielding Rib As described above, in this embodiment, the support plate 406 as the support member is formed of a metal (sheet metal) which is a conductor. Here, the bearing member 402 is provided adjacent to an end portion of the secondary transfer roller 41 in the rotational axis direction of the secondary transfer roller 41 in order to support the end portion in the rotational axis direction of the secondary transfer roller 41. Further, a compression spring 400 for pressing the bearing member 402 is also provided adjacent to an end portion of the secondary transfer roller 41 in the rotational axis direction of the secondary transfer roller 41. Further, an arm member 407 and a cam 409 for moving the bearing member 402 are also provided adjacent to an end portion of the secondary transfer roller 41 in the rotational axis direction of the secondary transfer roller 41. Further, from the viewpoint of workability when attaching, for example, an arm shaft 408 and a cam shaft 410, the support plate 406 for supporting the arm member 407 and the cam 409 is also provided adjacent to an end portion of the secondary transfer roller 41 in the rotational axis direction of the secondary transfer roller 41. Therefore, the support plate 406 and the compression spring 400 are arranged close to each other adjacent to an end portion of the rotational axis of the secondary transfer roller 41. And at the time of secondary transfer, a secondary transfer voltage is applied to the secondary transfer roller 41 via the compression spring 400 which is a conductor functioning as a power supply member. Therefore, there is a possibility that discharge occurs between the support plate 406 and the compression spring 400, or insulation degradation of the resin member around the support plate 406 and the compression spring 400 occurs. Even when the support plate 406 and the compression spring 400 are arranged apart from each other so as to sufficiently suppress discharge, it is important from the viewpoint of extending the service life of the secondary transfer unit 40 and the like to sufficiently suppress the insulation degradation over time of the insulator existing between the support plate 406 and the compression spring 400.

[0060] FIG. 11 is a schematic cross-sectional view seen from the direction opposite to the pressing direction (Z direction) along the pressing direction of the compression spring 400, that is, in a direction substantially perpendicular to the spring seat surface 417 in the vicinity of the compression spring 400 of the secondary transfer unit 40. Note that FIG. 11 shows a configuration in which a shielding rib 415 (FIGS. 12 and 13), which will be described later, is not provided for convenience of explanation.

[0061] As described above, during the secondary transfer, a secondary transfer voltage is applied to the pressure spring 400 which is a conductor. On the other hand, the support plate 406 is formed of sheet metal which is a conductor and is electrically grounded. And these two conductors are arranged within a short space distance. Therefore, when the shortest distance between these two conductors along the surface of the insulator (in this embodiment, the holder 404 which is a resin member) existing between these two conductors, that is, the creepage distance cannot be sufficiently ensured, insulation deterioration may occur in this insulator over time, and the electrical resistance value may decrease. As a result, it becomes difficult to apply the desired secondary transfer voltage to the secondary transfer roller 41, and the life of the secondary transfer unit 40 may be shortened. In particular, in this embodiment, the space S2 including the shortest distance along the surface of the holder 404 between the support plate 406 and the pressure spring 400 cannot isolate the space by providing a partition wall. This is because a clearance is required for the operation of the bearing member 402 during the contact / separation operation of the secondary transfer roller 21 with respect to the intermediate transfer belt 21. Therefore, it is necessary to provide a sufficient creepage distance between the support plate 406 and the pressure spring 400 along the surface of the holder 404 included in this space S2. The creepage distance is defined by the surface distance of the insulator on the shortest distance between the pressure spring 400 and the support plate 406.

[0062] Therefore, in this embodiment, the secondary transfer unit 40 is configured such that a shielding rib 415 (FIGS. 12 and 13), which is a rib-shaped portion satisfying the condition of the creepage distance capable of sufficiently suppressing the above-described insulation deterioration, is provided on the spring seat surface 417 of the holder 404 between the pressure spring 400 and the support plate 406.

[0063] FIG. 12 is a schematic cross-sectional view showing an enlarged view of the vicinity of the pressure spring 400 of the secondary transfer unit 40 as seen from the direction opposite to the pressure application direction (Z direction) along the direction substantially perpendicular to the spring seat surface 417, that is, along the pressure application direction of the pressure spring 400.

[0064] In this embodiment, when viewed along the pressurizing direction of the pressurizing spring 400, the holder 404 has a shielding rib 415 located on a spring seat surface 417 positioned between the pressurizing spring 400 and the support plate 406, and the shielding rib 415 extends along the pressurizing direction (-Z direction) of the pressurizing spring 400 from the spring seat surface 417. In this embodiment, the shielding rib 415 extends so as to protrude in a direction substantially perpendicular to the spring seat surface 417 from the spring seat surface 417. Further, in this embodiment, the shielding rib 415 has a gap from the pressurizing spring 400 in the radial direction of the pressurizing spring 400 and covers a part of the periphery of the pressurizing spring 400 in an arc shape along the circumferential direction of the pressurizing spring 400. Here, when viewed along the pressurizing direction of the pressurizing spring 400, the angular region where a creepage distance is required on the surface of the holder 404, which is an insulator, is determined as a region G surrounded by a straight line obtained by subtracting ±45° from a straight line passing through the shortest distance between the pressurizing spring 400 and the support plate 406, that is, a straight line passing through the closest part P1 of the support plate 406 to the pressurizing spring 400 and the closest part P2 of the pressurizing spring 400 to the support plate 406 (the dashed-dotted line E-E' in FIG. 12). This angular region G is an angular range centered on the closest part P2 of the pressurizing spring 400 to the support plate 406. The shielding rib 415 needs to be provided at least on the spring seat surface 417 of the holder 404 between the pressurizing spring 400 and the support plate 406 on the above straight line. More preferably, the shielding rib 415 is provided so as to be able to shield the periphery of the pressurizing spring 400 over at least the above angular region G (±45° with respect to the straight line passing through the shortest distance). The shielding rib 415 may be provided so as to shield the periphery of the pressurizing spring 400 over a range wider than the above angular region G (±45° with respect to the above straight line). However, it can be said that a region within ±90° with respect to the above straight line is often sufficient. Note that the shielding rib 415 may be provided so as to surround the entire circumference of the pressurizing spring 400.

[0065] Here, as shown in FIG. 11, for the space S1 including the shortest distance between the support plate 406 and the power supply spring 403, the space in which these two are arranged is isolated by the partition wall 412 provided in the holder 404. Therefore, for this space S1, the creepage distance is unnecessary. However, at least a part of the power supply spring 403 disposed on the spring seat surface 417 in the vicinity of the contact portion with the compression spring 400 faces the support plate 406 through the aforementioned space S2. Therefore, an additional shielding rib may be provided on the spring seat surface 417 of the holder 404 located between the power supply spring 403 and the support plate 406 when viewed along the compression direction of the compression spring 400. That is, as shown in FIG. 13, when the portion corresponding to the shielding rib 415 shown in FIG. 12 is the first shielding portion 415a, the shielding rib 415 may further have a second shielding portion 415b that shields the space between the power supply spring 403 and the support plate 406. For example, as shown in FIG. 13, the shielding rib 415 may have a rib shape having the second shielding portion 415b so as to connect the first shielding portion 415a and the partition wall 412. That is, the shielding rib 415 may have a rib shape in which the second shielding portion 415b and the first shielding portion 415a are continuous from the partition wall 412.

[0066] Note that the power supply member for supplying power to the compression spring 400 such as the power supply spring 403 has relatively high freedom of arrangement. Therefore, when the power supply member for supplying power to the compression spring 400 such as the power supply spring 403 is sufficiently separated from the support plate 406, an additional shielding rib (second shielding portion) that shields the space between the power supply spring 403 and the support plate 406 may not be provided.

[0067] Next, the height of the shielding rib 415 (the first shielding portion 415a and the second shielding portion 415b) will be described. FIG. 14 is a schematic cross-sectional view taken in the direction of the arrow in FIG. 12 (FIG. 13) with the dashed-dotted line E-E' in FIG. 12 (or FIG. 13) as the cutting line. The height R of the shielding rib 415 is set to provide a sufficient creepage distance between the pressure spring 400 and the support plate 406 and not to interfere with the movement of the bearing member 402 when the secondary transfer roller 41 makes a contact / separation operation with respect to the intermediate transfer belt 21. As shown in FIG. 14, in this embodiment, the height R of the shielding rib 415 is set so as to maintain a sufficient clearance so as not to interfere with the bearing member 402 even when the bearing member 402 moves in the direction along the pressing direction of the pressure spring 400 (the direction along the Z direction). That is, the height R of the shielding rib 415 is set to provide a sufficient creepage distance between the pressure spring 400 and the support plate 406 and to be sufficiently shorter than the length in the expansion / contraction direction of the pressure spring 400 in a state where the secondary transfer roller 41 is separated from the intermediate transfer belt 21 (for example, to a length of half or less).

[0068] Next, the necessary creepage distance between the compression spring 400 and the support plate 406 in this embodiment will be further described. FIG. 15 is a schematic cross-sectional view enlarged in the vicinity of the shielding rib 415 (FIG. 12 or FIG. 13) and viewed from the same direction as FIG. 12 (or FIG. 13). Here, as described above, the creepage distance is defined as the surface distance of the insulator on the shortest distance between the compression spring 400 and the support plate 406. Therefore, the creepage distance when the shielding rib 415 is not provided can be represented by a dotted arrow D4 in FIG. 15, starting from the point on the surface of the compression spring 400 on the shortest distance and ending at the point on the surface of the holder 404 closest to the support plate 406 (D6 in FIG. 15). The length of the dotted arrow D4 when the shielding rib 415 is not provided is insufficient as a creepage distance that can sufficiently suppress insulation degradation. On the other hand, the creepage distance when the shielding rib 415 is provided is represented by "D7 + R", where D7 is the length of the dotted arrow D7 in FIG. 15, starting from the point on the surface of the shielding rib 415 closest to the compression spring 400 (D5 in FIG. 15) and ending at the point on the surface of the holder 404 closest to the support plate 406 (D6 in FIG. 15), plus the height R (FIG. 14) of the shielding rib 415. In this embodiment, this distance "D7 + R" is long enough as a creepage distance that can sufficiently suppress insulation degradation. Thereby, it is possible to reduce the possibility that the life of the secondary transfer unit 40 is shortened due to insulation degradation.

[0069] As described above, in this embodiment, the image forming apparatus 100 includes an image carrier (photosensitive drum) 1 that carries a toner image, an intermediate transfer belt 21 that is stretched over a plurality of stretching rollers and to which the toner image is transferred from the image carrier 1, a transfer roller (secondary transfer roller) 41 that can contact the outer peripheral surface of the intermediate transfer belt 21 and forms a transfer nip portion (secondary transfer nip portion) N2 that cooperates with an opposing roller (secondary transfer opposing roller) 22 among the plurality of stretching rollers to transfer the toner image from the intermediate transfer belt 21 to the recording material P, a bearing member 402 made of an electrically insulating resin that supports an end portion of the transfer roller 41 in the rotational axis direction, a pressurizing spring 400 that pressurizes the bearing member 402 so as to pressurize the transfer roller 41 against the intermediate transfer belt 21, a holding member (holder) 404 that holds the bearing member 402 so as to be movable between a first position where the transfer roller 41 contacts the intermediate transfer belt 21 and a second position where the transfer roller 41 is separated from the intermediate transfer belt 21 along the pressurizing direction of the pressurizing spring 400, an arm member 407 that can engage with the bearing member 402 and moves the bearing member 402 from the first position to the second position against the pressurizing force of the pressurizing spring 400, a support member (support plate) 406 made of metal that rotatably supports the arm member 407, an applying portion (secondary transfer power source) 34 that applies a voltage to the transfer roller 41 through the pressurizing spring 400, and a connecting member (power supply chip) 500 that electrically connects the pressurizing spring 400 and the transfer roller 41. The pressurizing spring 400 is disposed between a receiving portion (first receiving portion) 422 provided on the bearing member 402 and a spring support portion 405 provided on the holding member 404. When viewed along the pressurizing direction of the pressurizing spring 400, the closest portion P1 of the support member 406 to the pressurizing spring 400 is disposed adjacent to a spring seat surface 417 which is the surface where the spring support portion 405 of the holding member 404 is provided. The holding member 404 has a rib-shaped portion (shielding rib) 415 that extends along the pressurizing direction of the pressurizing spring 400 from the spring seat surface 417 between the pressurizing spring 400 and the support member 406 on a straight line (on the shortest distance between the pressurizing spring 400 and the support member 406 passing through the closest portion P1 of the support member 406 to the pressurizing spring 400 and the closest portion P2 of the pressurizing spring 400 to the support member 406 when viewed along the pressurizing direction of the pressurizing spring 400).

[0070] Here, when viewed in the pressing direction of the pressing spring 400, the rib-shaped portion 415 is preferably provided so as to be located between the pressing spring 400 and the support member 406 in an angular region G of ±45° from the above straight line around the closest portion P2 to the support member 406 of the pressing spring 400 at least. Further, the image forming apparatus 100 may have a power supply member (power supply spring) 403 that is at least partially disposed on the spring seat surface 417 and supplies power from the application unit 34 to the pressing spring 400. In this case, the rib-shaped portion 415 may be further provided so as to be located between the power supply member 403 disposed on the spring seat surface and the support member 406 (on the shortest distance between the power supply member 403 and the support member 406 via the surface of the spring seat surface 417) when viewed along the pressing direction of the pressing spring 400. Also, in the present embodiment, the transfer roller 41 includes a shaft portion 41b protruding from an end portion in the rotation axis direction thereof, a bearing 401 is attached to the shaft portion 41b, and the connection member 500 electrically connects the pressing spring 400 and the transfer roller 41 via the bearing 401. Further, in the present embodiment, the image forming apparatus 100 has a cam 409 that rotates the arm member 407, and the support member 406 rotatably supports the cam 409.

[0071] As described above, in the present embodiment, by adopting a configuration in which the bearing member 402 is moved by the arm member 407, it is possible to achieve space saving in a configuration that separates the secondary transfer roller 41 from the intermediate transfer belt 21. Also, by forming the support plate 406 from metal, it is possible to reduce the possibility of a decrease in product life due to breakage of the support member that supports the arm member, or a decrease in the unintended separation distance due to deformation of the support member, thereby achieving a longer life of the secondary transfer unit 40. And by providing the shielding rib 415 on the spring seat surface 417 of the holder 404, it is possible to reduce the risk of occurrence of insulation degradation of the insulator between the support plate 406 and the pressing spring 400.

[0072] [Embodiment 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed descriptions thereof are omitted.

[0073] FIG. 16 is a schematic cross-sectional view taken from the same direction as FIG. 11, showing an enlarged view of the vicinity of the space S2 in FIG. 11 described in the first embodiment. Similar to FIG. 11, FIG. 16 shows a configuration in which the shielding ribs (FIGS. 12 and 13) described in the first embodiment are not provided. FIG. 16(a) shows a state in which the secondary transfer roller 41 is in contact with the intermediate transfer belt 21, and FIG. 16(b) shows a state in which the secondary transfer roller 41 is separated from the intermediate transfer belt 21. Further, FIG. 17 is a schematic cross-sectional view of the cross section at the position of the dashed-dotted line C-C' in FIG. 11 as viewed from the direction of the arrow in FIG. 11. FIG. 17(a) shows a state in which the secondary transfer roller 41 is in contact with the intermediate transfer belt 21, and FIG. 17(b) shows a state in which the secondary transfer roller 41 is separated from the intermediate transfer belt 21.

[0074] When the bearing member 402 is moved in a direction opposite to the pressing direction of the compression spring 400 (Z direction) by the arm member 407 of the approaching / separating mechanism 425 (Figs. 9 and 10), the secondary transfer roller 41 shown in Figs. 16(a) and 17(a) comes into contact with the intermediate transfer belt 21, and then the secondary transfer roller 41 shown in Figs. 16(b) and 17(b) is separated from the intermediate transfer belt 21. At this time, a moment is generated due to the inclination of the compression spring 400 or the like, and the bearing member 402 inclines along the direction intersecting the moving direction, that is, the Y direction (this is also referred to as "tilting in the Y direction"). In this embodiment, the pressing surface 411 of the bearing member 402 is located on the central side in the rotational axis direction of the secondary transfer roller 41 and on the side opposite to the pressing direction of the compression spring 400 (the lower side in Fig. 17) with respect to the spring seat surface 417 of the holder 404. Therefore, during the above movement, the bearing member 402 inclines along the Y direction such that, for example, the side of the secondary transfer roller 41 moves to the central side in the rotational axis direction of the secondary transfer roller 41 and the side of the pressing surface 411 moves to the end side in the rotational axis direction of the secondary transfer roller 41. Thus, when the bearing member 402 tilts in the Y direction when the secondary transfer roller 41 is separated from the intermediate transfer belt 21, there is a possibility that the moving amount of the bearing member 402 in the Z direction, that is, the separation amount of the secondary transfer roller 41 from the intermediate transfer belt 21, may be unintentionally reduced.

[0075] Therefore, in the present embodiment, a regulating rib 414 as a regulating portion having a function of restricting the Y-direction fall of the bearing member 402 is provided on the holder 404. The regulating rib 414 is continuous from the spring seat surface 417 of the holder 404, and is provided on an opposing surface 416 which is a surface extending along the pressing direction of the pressing spring 400 (the moving direction of the bearing member 402) on the side opposite to the pressing direction of the pressing spring 400 with respect to the spring seat surface 417. This opposing surface 416 faces the bearing member 402 regardless of whether the bearing member 402 is in the first position where the secondary transfer roller 41 contacts the intermediate transfer belt 21 or the second position where the secondary transfer roller 41 is separated from the intermediate transfer belt 21. In the present embodiment, two regulating ribs 414 are provided (see FIG. 11). Further, in the present embodiment, these two regulating ribs 414 are linear rib-shaped portions extending substantially parallel to each other along the pressing direction of the pressing spring 400, and protrude from the opposing surface 416 toward the central side in the rotational axis direction of the secondary transfer roller 41. Thereby, the fall of the bearing member 402 in the Y direction when the secondary transfer roller 41 moves away from the intermediate transfer belt 21 is restricted, and it is possible to suppress the unintentional reduction of the amount of movement of the bearing member 402 in the Z direction, that is, the separation amount of the secondary transfer roller 41 from the intermediate transfer belt 21.

[0076] Here, as described in the first embodiment, the bearing member 402 and the support plate 406 are arranged in proximity to each other on the end side in the rotational axis direction of the secondary transfer roller 41. And when the bearing member 402 is configured to contact the regulating rib 414 of the holder 404 as described above, in the space S2 shown in FIG. 11, a desirable path may occur that provides a sufficient creepage distance between the support plate 406 and the pressing spring 400, separate from the path (D4 in FIG. 15) described in the first embodiment.

[0077] As described in Example 1, the required creepage distance is defined by the surface distance of the insulator on the shortest distance between the compression spring 400 and the support plate 406. As shown in FIG. 16(b), when the bearing member 402 is in contact with the regulating rib 414, specifically, starting from a point on the surface of the compression spring 400, passing through the regulating rib 414 of the holder 404, and ending at a point on the surface of the bearing member 402 closest to the support plate 406 (D1 in FIG. 16(b)), it can be represented by the dotted arrow D2 in FIG. 16(b). It is considered that the length of the dotted arrow D2 when the regulating rib 414 and the bearing member 402 are in contact is insufficient as the creepage distance that can sufficiently suppress insulation degradation.

[0078] On the other hand, if the regulating rib 414 and the bearing member 402 are not in contact and there is a space between them, it is not necessary to consider the creepage distance of the path passing through the regulating rib 414.

[0079] Therefore, in this embodiment, the secondary transfer unit 40 is configured such that the contact / non-contact relationship between the regulating rib 414 and the bearing member 402 changes as follows. That is, in the state where the secondary transfer roller 41 shown in FIGS. 16(a) and 17(a) is in contact with the intermediate transfer belt 21, the bearing member 402 is not in contact with the regulating rib 414 and there is a space between them. Therefore, as described above, it is not necessary to consider the creepage distance of the path passing through the regulating rib 414. On the other hand, in the state where the secondary transfer roller 41 shown in FIGS. 16(b) and 17(b) is separated from the intermediate transfer belt 21, the bearing member 402 abuts on the regulating rib 414. However, in this embodiment, when the secondary transfer roller 41 is separated from the intermediate transfer belt 21, the printing operation is not performed and no voltage is applied to the secondary transfer roller 41. That is, in this embodiment, when the control unit 120 controls the contact / separation mechanism 425 to make the secondary transfer roller 41 separated from the intermediate transfer belt 21, the secondary transfer power supply 34 is controlled so as not to apply a voltage to the secondary transfer roller 41. Therefore, in this embodiment, the secondary transfer unit 40 is configured to be able to suppress insulation degradation in the path passing through the regulating rib 141 in either the state where the secondary transfer roller 41 is in contact with or separated from the intermediate transfer belt 21.

[0080] Note that, as described above, FIGS. 11 and 16 showed the configuration in which the shielding rib 415 described in Example 1 was not provided, but the shielding rib 415 may be provided. Also in this case, according to the configuration of the present embodiment, insulation degradation in the path via the regulating rib 414 can be more reliably suppressed. Further, when the creepage distance in the path described in Example 1 is sufficient, by applying the configuration of the present embodiment to the configuration in which the shielding rib 415 described in Example 1 is not provided, insulation degradation in the path via the regulating rib 414 can be suppressed.

[0081] As described above, in the present embodiment, the holding member 406 is a surface that is continuous from the spring seat surface 417 and extends in a direction along the moving direction of the bearing member 402 by the arm member 407, and is a surface that faces the bearing member 402 in any of the first position (the position where the secondary transfer roller 41 contacts the intermediate transfer belt 21) and the second position (the position where the secondary transfer roller 41 is separated from the intermediate transfer belt 21) of the bearing member 402. The regulating portion (regulating rib) 414 that regulates the movement of the bearing member 402 in the direction approaching the spring seat surface 417 of the bearing member 402, and the regulating portion 414 is provided so as not to contact the bearing member 402 when the bearing member 402 is in the first position and to contact the bearing member 402 when the bearing member 402 is in the second position. The image forming apparatus 100 has a control unit 120 that controls the applying unit 34 so as not to apply a voltage to the transfer roller 41 when the bearing member 402 is in the second position.

[0082] As described above, according to the present embodiment, the fall of the bearing member 402 can be suppressed by the regulating rib 141, and insulation degradation in the path via the regulating rib 141 can be suppressed.

[0083] [Others] As described above, the present invention has been described with reference to specific embodiments, but the present invention is not limited to the above-described embodiments.

[0084] In the above-described embodiments, the bearing was a ball bearing, but the present invention is not limited thereto. For example, a ball bearing, a roller bearing, etc., which are typically rolling bearings, can be appropriately used. Further, the bearing member may be configured to directly support the shaft portion of the secondary transfer roller rotatably without using a bearing.

[0085] Also, in the above-described embodiments, an example in which the secondary transfer roller is separated from the intermediate transfer belt in the standby state or when the power is turned off of the image forming apparatus has been described, but the present invention is not limited thereto. For example, when the test image formed on the intermediate transfer belt passes through the position corresponding to the secondary transfer nip portion, the secondary transfer roller may be separated from the intermediate transfer belt. Also in this case, when the secondary transfer roller is separated from the intermediate transfer belt, a voltage can be prevented from being applied to the secondary transfer roller.

[0086] Also, in the above-described embodiments, the connecting member that electrically connects the pressure spring and the secondary transfer roller was configured to press the secondary transfer roller, but the present invention is not limited thereto. The connecting member does not have to be configured to press the secondary transfer roller as long as it can electrically connect the pressure spring and the secondary transfer roller.

[0087] Also, in the above-described embodiments, the support member that supports the arm member was made of sheet metal, but the present invention is not limited thereto. The support member does not have to be a plate-shaped member as long as it is made of metal.

[0088] Note that an insulator refers to a substance having a volume resistivity of 10 8 (Ω·m) or more, preferably 10 10 (Ω·m) or more. However, typically, an insulator has a volume resistivity of 10 16 (Ω·m) or less. Also, a conductor refers to a substance having a volume resistivity of 10 -6 (Ω·m) or less, typically about 10 -8 (Ω·m).

Description of Reference Numerals

[0089] 21 Intermediate transfer belt 40 Secondary transfer unit 41 Secondary transfer roller (secondary transfer roller) 100 Image forming apparatus 400 Pressure spring (pressing member) 401 Bearing 402 Bearing member 403 Power supply spring (power supply member) 404 Holder (holding member) 405 Spring support portion 406 Support plate (support member) 407 Arm member 414 Regulation rib 415 Shielding rib 417 Spring seating surface 500 Power supply chip (connection member)

Claims

1. An image carrier that carries a toner image, An intermediate transfer belt stretched over a plurality of stretching rollers, onto which the toner image is transferred from the image carrier, A transfer roller that can contact the outer peripheral surface of the intermediate transfer belt and forms a transfer nip portion in cooperation with an opposing roller among the plurality of stretching rollers, where the toner image is transferred from the intermediate transfer belt to a recording material, A bearing member made of an electrically insulating resin that supports an end portion of the transfer roller in the axial direction of the rotation axis thereof, A pressure spring that pressurizes the bearing member so as to press the transfer roller against the intermediate transfer belt, A holding member that holds the bearing member so as to be movable along the pressurizing direction of the pressure spring between a first position where the transfer roller contacts the intermediate transfer belt and a second position where the transfer roller is separated from the intermediate transfer belt, An arm member that can engage with the bearing member and moves the bearing member from the first position to the second position against the pressurizing force of the pressure spring, A support member made of metal that rotatably supports the arm member, An application unit that applies a voltage to the transfer roller through the pressure spring, A connection member that electrically connects the pressure spring and the transfer roller, characterized by comprising: The pressure spring is disposed between a receiving portion provided on the bearing member and a spring support portion provided on the holding member, When viewed along the pressurizing direction of the pressure spring, the closest portion of the support member to the pressure spring is disposed adjacent to a spring seat surface, which is the surface on which the spring support portion of the holding member is provided, The holding member has a rib-shaped portion that extends along the pressurizing direction of the pressure spring between the pressure spring and the support member on a straight line passing through the closest portion of the support member to the pressure spring and the closest portion of the pressure spring to the support member when viewed along the pressurizing direction of the pressure spring, starting from the spring seat surface. An image forming apparatus characterized by this.

2. The image forming apparatus according to claim 1, characterized in that the rib-shaped portion is provided so as to be located between the pressure spring and the support member in an angular region of ±45° from the straight line around at least the closest portion of the pressure spring to the support member when viewed in the pressurizing direction of the pressure spring.

3. Characterized by having a power supply member that at least partially is disposed on the spring seat surface and supplies power from the application unit to the pressure spring. The rib-shaped portion is further provided so as to be located between the power supply member and the support member disposed on the spring seat surface when viewed along the pressing direction of the pressing spring. The image forming apparatus according to claim 1, characterized in that.

4. The holding member is a surface that is continuous from the spring seat surface and extends in a direction along the moving direction of the bearing member by the arm member, and the bearing member is in any of the first position and the second position. The opposing surface that faces the bearing member also has a restricting portion that restricts the movement of the bearing member in the direction approaching the spring seat surface of the bearing member. The restricting portion is provided so as not to contact the bearing member when the bearing member is in the first position, and to contact the bearing member when the bearing member is in the second position. The image forming apparatus has a control portion that controls the applying portion so as not to apply a voltage to the transfer roller when the bearing member is in the second position. The image forming apparatus according to claim 1, characterized in that.

5. The transfer roller includes a shaft portion protruding from an end portion in the rotation axis direction thereof, a bearing is attached to the shaft portion, and the connecting member electrically connects the pressing spring and the transfer roller via the bearing. The image forming apparatus according to claim 1, characterized in that.

6. It has a cam that rotates the arm member. The support member rotatably supports the cam. The image forming apparatus according to claim 1, characterized in that.

Images