Transfer apparatus, image forming apparatus

Abstract

To appropriately separate an intermediate transfer body from latent image carriers.SOLUTION: A transfer device comprises: an intermediate transfer belt 2 that travels in a loop; a plurality of primary transfer units that have primary transfer rollers and transfer toner images to the intermediate transfer belt; a driven roller 33A that is arranged on the downstream side of a most downstream primary transfer roller 7T of a most downstream primary transfer unit 203, and stretches the intermediate transfer belt; a first moving mechanism that moves the driven roller to change a position where the driven roller stretches the intermediate transfer belt; and a second moving mechanism that can move the primary transfer roller arranged on the upstream side of the most downstream primary transfer unit to a contact position where it is in contact with a photoreceptor with the intermediate transfer belt therebetween and to a separation position where it is separated from the photoreceptor. The most downstream primary transfer roller is provided to be movable to a contact position where it is in contact with the photoreceptor with the intermediate transfer belt therebetween and to a separation position where it is separated from the photoreceptor. The first moving mechanism moves the driven roller to at least three positions for stretching the intermediate transfer belt.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] In an image forming apparatus capable of printing a color image, in addition to the four colors of YMCK, a transfer device capable of transferring special color toners such as a transparent color and a white color is provided. In such an image forming apparatus, first, toner images of each color are transferred to an intermediate transfer body in each primary transfer unit, and then a multicolor toner image is secondarily transferred to a recording sheet such as paper in the secondary transfer unit.

[0003] For example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-30737), in addition to the four colors of YMCK, a primary transfer unit for transferring a transparent color toner image is provided at the most downstream of an intermediate transfer belt. When a transparent toner image is not formed, the transfer roller of the primary transfer unit corresponding to the transparent color is separated from the photoreceptor, and the toner image forming unit for the transparent toner stops. Thus, by separating the transfer roller corresponding to the special color toner from the photoreceptor as the latent image carrier when the special color toner image is not formed, excessive consumption of the special color toner can be suppressed.

[0004] However, in a configuration in which the primary transfer members of the primary transfer units other than the primary transfer unit for transferring the transparent color toner image are moved into and out of contact, the position where the intermediate transfer body is stretched also changes depending on the arrangement of these primary transfer members. Therefore, even if the primary transfer member at the most downstream is separated from the intermediate transfer body, the intermediate transfer body cannot be appropriately separated from the latent image carrier, and there is a problem that it causes damage to the intermediate transfer body and the latent image carrier.

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object is to appropriately separate the intermediate transfer body from the latent image carrier.

Means for Solving the Problems

[0006] To solve the above problems, the present invention provides a plurality of primary transfer units having a circulating intermediate transfer body and a primary transfer member, which transfer a developer image to the intermediate transfer body, a first tension roller positioned downstream of the downstream primary transfer member, which is the primary transfer member of the downstream primary transfer unit, which is positioned furthest downstream in the direction of travel of the intermediate transfer body, and which tensions the intermediate transfer body, a first moving mechanism that moves the first tension roller and changes the position in which the first tension roller tensions the intermediate transfer body, and the primary transfer member of the primary transfer unit positioned upstream of the downstream primary transfer unit in the direction of travel of the intermediate transfer body The upstream primary transfer member via the intermediate transfer body Latent image carrier A transfer apparatus comprising a second moving mechanism that is movable between a contact position in contact with the latent image carrier and a separated position away from the latent image carrier, wherein the downstream primary transfer member is provided to be movable between a contact position in contact with the latent image carrier via the intermediate transfer body and a separated position away from the latent image carrier, and the first tension roller tensions the intermediate transfer body by the first moving mechanism. First position, second position, third position Move to at least three positions, In the direction of the primary transfer member's contact with the latent image carrier, the distance of the first tension roller from the latent image carrier increases in the order of the first position, the second position, and the third position. When the downstream primary transfer member is in contact with the carrier, the first tension roller is positioned at the first position. When the downstream primary transfer member is in the separated position and the upstream primary transfer member is in the separated position, the first tension roller is positioned at the second position. When the downstream primary transfer member is in the separated position and the upstream primary transfer member is in contact with the carrier, the first tension roller is positioned at the third position. It is characterized by the following: [Effects of the Invention]

[0007] According to the present invention, the intermediate transfer body can be appropriately separated from the latent image carrier. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram of the image forming apparatus. [Figure 2] This is a schematic diagram of a transfer apparatus according to one embodiment of the present invention. [Figure 3] (a) to (f) are diagrams showing the transfer apparatus in each mode from A to F. [Figure 4] This diagram shows how to switch between each mode. [Figure 5] This diagram shows the configuration of the drive source for the contact / separation mechanism, viewed from the front of the image forming apparatus, in the "small separation" state. [Figure 6]Figure 5 shows a perspective view with the bracket removed. [Figure 7] This diagram shows the configuration of the drive source for the contact / separation mechanism, viewed from the front of the image forming apparatus, in the "contact" state. [Figure 8] This diagram shows the configuration of the drive source for the contact / separation mechanism, viewed from the front of the image forming apparatus, in the "large separation" state. [Figure 9] This diagram shows the contact and separation configuration of the downstream primary transfer section with respect to the intermediate transfer belt, as viewed from the back side of the image forming apparatus, illustrating the "contact" state. [Figure 10] This diagram shows the contact and separation configuration of the downstream primary transfer section with respect to the intermediate transfer belt, as viewed from the back side of the image forming apparatus, in the "small separation" state. [Figure 11] This diagram shows the contact and separation configuration of the downstream primary transfer section with respect to the intermediate transfer belt, as viewed from the back side of the image forming apparatus, in the "large separation" state. [Figure 12] This is a perspective view showing the cam component. [Figure 13] This is a perspective view of the cam component and its surrounding structure, seen from the rear side. [Figure 14] This is a plan view showing the configuration around the first and second arms. [Figure 15] This is a perspective view showing the configuration of the second arm and its surrounding area. [Figure 16] This is a perspective view of the second arm and its surrounding components, seen from the rear. [Figure 17] This is a plan view showing the contact and separation configuration of the detection sensor and sensor bracket. [Figure 18] This is a perspective view of the first sensor bracket and the second sensor bracket as seen from the front side of the image forming apparatus. [Figure 19] This is a plan view showing the positioning of the second sensor bracket in the "large separation" state. [Figure 20] This is a plan view showing the contact and separation configuration between the central primary transfer unit and the uppermost primary transfer section and the intermediate transfer belt. [Figure 21]The figure shows the layout of the image forming unit, the reservoir before replenishment, and the toner bottle when a special color toner is placed in the lowermost primary transfer unit. [Figure 22] The figure shows the layout of the image forming unit, the reservoir before replenishment, and the toner bottle when black toner is placed in the lowermost primary transfer unit. [Figure 23] The figure shows the configuration of the toner supply device. [Figure 24] The flowchart is for checking the layout of the image forming unit, the reservoir before replenishment, and the toner bottle. [Figure 25] The schematic diagram shows the configuration of the control unit provided in the image forming apparatus. [Figure 26] The plan view shows the layout of the driven roller and the detection sensor in an embodiment different from FIG. 5. [Figure 27] The plan view shows the contact and separation configuration of the central primary transfer unit in an embodiment different from FIG. 5. Diagram (a) shows the "contact" state, and diagram (b) shows the "separated" state. [Figure 28] The plan view shows the contact and separation configuration of the lowermost primary transfer unit in an embodiment different from FIGS. 5 and 27. Diagram (a) shows the "contact" state, diagram (b) shows the "small separation" state, and diagram (c) shows the "large separation" state. [Figure 29] The plan view shows the layout of the lowermost primary transfer roller of the transfer device in an embodiment different from FIGS. 5, 27, and 28 in the contact state. [Figure 30] The plan view shows the rotation mechanism for rotating the tension roller. Diagram (a) shows the layout in the state where the lowermost primary transfer roller is in contact, and diagram (b) shows the layout in the state where the lowermost primary transfer roller and the central primary transfer roller are separated.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and the redundant description will be simplified or omitted as appropriate.

[0010] Figure 1 shows the configuration of an image forming apparatus 1 according to one embodiment of the present invention. The image forming apparatus 1 shown in Figure 1 is a color printer with a tandem configuration in which multiple photoreceptors as latent image carriers are arranged side by side. Each photoreceptor can form a toner image of a color corresponding to color separation using toner as a developer supplied from a developing device. After superimposing and transferring the toner images formed on each photoreceptor onto an intermediate transfer surface, the superimposed image is transferred all at once to a sheet such as recording paper, thereby forming a multicolor image on the sheet. In the present invention, the image forming apparatus is not limited to a color printer, but also includes color copiers, facsimile machines, and printing presses, among others.

[0011] In Figure 1, the image forming apparatus 1 has an image forming unit 1A positioned near the center in the vertical direction, a paper feeding unit 1B below it, and a document scanning unit 1C equipped with a document placement table 1C1 positioned above the image forming unit 1A. An intermediate transfer belt 2, which serves as an intermediate transfer body, is positioned in the image forming unit 1A. The intermediate transfer belt 2 has a horizontally stretched surface. Above the intermediate transfer belt 2, a configuration is provided for forming an image of a color with a color separation color and a complementary color.

[0012] The image forming unit 1A is equipped with image forming units 10K, 10C, 10M, 10Y, and 10T, which are capable of forming images using complementary color toners (yellow, magenta, cyan, and black) and glossy images using transparent toner. Each image forming unit 10K, 10C, 10M, 10Y, and 10T has a photoreceptor 3K, 3C, 3M, 3Y, and 3T (transparent toner) capable of carrying an image, which is arranged side by side along the tensioned surface of the intermediate transfer belt 2. In the following description, if the content is common to all photoreceptors, the photoreceptor will be indicated by the reference numeral 3.

[0013] Each photoreceptor 3K, 3C, 3M, 3Y, and 3T consists of a drum that can rotate in the same direction (counterclockwise in Figure 1), and around it are a charging device, a writing device 5, a developing device 6, a primary transfer roller 7 as a primary transfer member, and a cleaning device that perform image formation processing during the rotation process (for convenience, the reference numeral T is added to the symbols of each device, with photoreceptor 3T as the target).

[0014] The transfer device 20 comprises an intermediate transfer belt 2, a plurality of primary transfer rollers 7 (for convenience, only the primary transfer roller 7T is shown with a reference numeral), and a plurality of rollers 2A to 2C, which serve as transfer members.

[0015] The intermediate transfer belt 2 sequentially transfers toner images from the imaging unit, which is equipped with each photoreceptor 3. The intermediate transfer belt 2 is wrapped around multiple rollers 2A to 2C, and multiple rollers not indicated in Figure 1, and can travel in a circular motion in the direction of the arrows in Figure 1. Rollers 2A and 2B tension the intermediate transfer belt 2 on both sides of the outer side in the direction of travel of the intermediate transfer belt 2 at opposing positions facing each photoreceptor 3 of the intermediate transfer belt 2. The secondary transfer opposing roller 2C faces the secondary transfer device 9 across the intermediate transfer belt 2.

[0016] The secondary transfer device 9 has a secondary transfer roller 9A. The secondary transfer roller 9A forms a secondary transfer nip between itself and the secondary transfer opposing roller 2C, with the intermediate transfer belt 2 in between. The secondary transfer opposing roller 2C is subjected to a secondary transfer bias of the same polarity as the toner, while the secondary transfer roller 9A is grounded. As a result, a secondary transfer field is formed in the secondary transfer nip that electrostatically moves the multicolor toner image on the intermediate transfer belt 2 from the belt side towards the secondary transfer roller 9A side. This secondary transfer nip transfers the multicolor toner image to the sheet that has been transported to the secondary transfer nip.

[0017] Recording sheets are fed from the paper feed unit 1B to the secondary transfer position. The paper feed unit 1B comprises multiple paper feed cassettes 1B1 and multiple transport rollers 1B2. The multiple transport rollers 1B2 are arranged in the transport path of the recording sheets fed from the paper feed cassettes 1B1.

[0018] The writing device 5 irradiates the photoreceptors 3K, 3C, 3M, 3Y, and 3T with writing light, forming an electrostatic latent image on the photoreceptors 3K, 3C, 3M, 3Y, and 3T corresponding to the image information. This image information is obtained by scanning the original document on the original document tray 1C1 of the original document scanning unit 1C, or from image information output from a computer.

[0019] The document scanning unit 1C is equipped with a scanner 1C2 and an automatic document feeder 1C3. The scanner 1C2 exposes and scans the document on the document tray 1C1. The automatic document feeder 1C3 is positioned on the upper surface of the document tray 1C1. The automatic document feeder 1C3 is configured to be able to flip the document as it is fed onto the document tray 1C1, allowing scanning of both the front and back sides of the document.

[0020] The electrostatic latent image formed on the photoreceptor 3 by the writing device 5 is processed into a visible image by the developing device 6 (indicated by the symbol 6T in Figure 1 for convenience) and primary transferred to the intermediate transfer belt 2. Once the toner images of each color are superimposed and transferred onto the intermediate transfer belt 2, they are collectively secondary transferred to the recording sheet by the secondary transfer device 9.

[0021] The second-transferred recording sheet has the unfixed image on its surface fixed by the fixing device 11. The fixing device 11 has a belt fixing structure that includes a fixing belt heated by a heating roller and a pressure roller that is in contact with the fixing belt. By providing a contact area between the fixing belt and the pressure roller, i.e., a nip area, the heating area on the recording sheet can be expanded compared to a hot roller fixing method.

[0022] The recording sheet that has passed through the fixing device 11 has its transport direction switched by a transport path switching claw located behind the fixing device 11. Specifically, the transport path switching claw selects the transport direction to either the transport path toward the paper discharge section 13 or the reverse transport path RP.

[0023] In the image forming apparatus 1 having the above configuration, an electrostatic latent image is formed on a uniformly charged photoreceptor 3 by exposure scanning of a document placed on the document placement table 1C1, or by image information from a computer. After the electrostatic latent image is processed into a visible image by the developing apparatus 6, the toner image is first transferred to the intermediate transfer belt 2.

[0024] The toner image transferred to the intermediate transfer belt 2 is transferred directly to the recording sheet fed from the paper feed unit 1B in the case of a single-color image, and in the case of a multi-color image, the primary transfer is repeated to superimpose the images before being transferred all at once to the recording sheet in a secondary transfer. After the secondary transfer, the recording sheet has the unfixed image fixed by the fuser unit 11 and is then fed to the paper discharge unit 13 or inverted and fed again towards the secondary transfer position.

[0025] In Figure 1, the intermediate transfer belt 2 is constructed by forming a single or multiple layer of PVDF (vinyldenine fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), etc., with conductive materials such as carbon black dispersed within it. The volume resistivity of the intermediate transfer belt 2 is set to 10 8 ~10 12 Ωcm, and surface resistivity of 10 9 ~10 13The resistance is adjusted to be within the range of Ωcm. A release layer may be coated onto the surface of the intermediate transfer belt 2 as needed. Suitable coating materials include, but are not limited to, fluororesins such as ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinyldenide fluoride), PEA (perfluoroalkoxy fluororesin), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), and PVF (vinyl fluoride). The intermediate transfer belt 2 can be manufactured by casting, centrifugal molding, etc., and its surface may be polished as needed. If the volume resistivity of the intermediate transfer belt 2 exceeds the above-mentioned range, the bias required for transfer becomes higher, leading to increased power costs, which is undesirable. Furthermore, the charge potential of the intermediate transfer belt 2 increases during the transfer process and transfer paper peeling process, and self-discharge becomes difficult, necessitating the provision of static elimination means. Furthermore, if the volume resistivity and surface resistivity fall below the above range, the charge potential decays more quickly, which is advantageous for static discharge, but the current during transfer flows in the surface direction, causing toner to splatter. Therefore, it is preferable that the volume resistivity and surface resistivity of the intermediate transfer belt 2 in this embodiment are within the above range. The volume resistivity and surface resistivity were measured by connecting an HRS probe (inner electrode diameter 5.9 mm, ring electrode inner diameter 11 mm) to a high-resistivity resistivity meter (Mitsubishi Chemical Corporation: High Resista IP), applying a voltage of 100 V (500 V for surface resistivity) to both sides of the intermediate transfer belt 2, and using the measured values ​​after 10 seconds.

[0026] The intermediate transfer belt 2 is wrapped around at least one pair of rollers, rollers 2A and 2B, and a secondary transfer opposing roller 2C located at the secondary transfer position. By setting the drive roller 2A to rotate clockwise, the intermediate transfer belt 2 can move in the direction of the arrow shown inside the intermediate transfer belt 2 in Figure 1. The transfer surface of the belt moving between rollers 2A and 2B faces the photoreceptors 3K, 3Y, 3C, 3M, and 3T of each imaging unit. At positions facing each photoreceptor across the intermediate transfer belt 2, primary transfer rollers 7 (indicated by the symbol 7T in Figure 1, referring to special toner) are positioned, which correspond to transfer members for electrostatically transferring the visible image on the photoreceptor.

[0027] The primary transfer roller 7 used in this embodiment is made by coating a foaming resin agent onto a metal core (iron, stainless steel, aluminum alloy, etc.). The thickness of the foaming resin agent is 2 mm to 10 mm. Known blade-shaped or brush-shaped transfer members can also be used.

[0028] In this embodiment, in addition to the toner used for full-color image formation, white toner is used to form a white background on the image. Alternatively, transparent toner may be used to improve the gloss and transferability of the image, and light cyan toner, light magenta toner, etc., may be selected to increase the color gamut. In some cases, metallic toners such as gold toner or silver toner may be used as a background to create colored metallic colors such as reddish-bronze or bronze.

[0029] As shown in Figure 2, the primary transfer roller 7T forms a special color transfer nip NT between itself and the photoreceptor 3T via the intermediate transfer belt 2. The primary transfer roller 7C forms a cyan transfer nip NC between itself and the photoreceptor 3C via the intermediate transfer belt 2. The primary transfer roller 7M forms a magenta transfer nip NM between itself and the photoreceptor 3M via the intermediate transfer belt 2. The primary transfer roller 7Y forms a yellow transfer nip NY between itself and the photoreceptor 3Y via the intermediate transfer belt 2. The primary transfer roller 7K forms a black transfer nip NK between itself and the photoreceptor 3K via the intermediate transfer belt 2.

[0030] The transfer device 20 includes an upstream primary transfer section 201 located on the upstream side in the direction of travel of the intermediate transfer belt 2, a downstream primary transfer section 203 located on the downstream side, and a central primary transfer unit 202 consisting of a plurality of primary transfer sections located between the upstream primary transfer section 201 and the downstream primary transfer section 203. In this embodiment, the upstream primary transfer section 201 transfers a black toner image using a black transfer nip NK, the central primary transfer unit 202 transfers cyan toner images, magenta toner images, and yellow toner images using cyan transfer nip NC, magenta transfer nip NM, and yellow transfer nip NY, and the downstream primary transfer section 203 transfers a special color toner image using a special color transfer nip NT, all to the intermediate transfer belt 2. In the following description, the upstream or downstream side in the direction of travel of the intermediate transfer belt 2 will also be simply referred to as the upstream side or the downstream side.

[0031] In Figure 2, the primary transfer roller 7K located in the uppermost primary transfer section 201 is the uppermost primary transfer member, the primary transfer rollers 7Y, 7M, and 7C located in the central primary transfer unit 202 are the central primary transfer members, and the primary transfer roller 7T located in the lowermost primary transfer section 203 is the lowermost primary transfer member. The direction of travel of the intermediate transfer belt 2 is indicated by arrow A in Figure 2. Furthermore, the primary transfer rollers 7K, 7Y, 7M, and 7C located upstream of the primary transfer roller 7T are also upstream primary transfer members.

[0032] In this embodiment, the special color can be transferred in either the uppermost primary transfer unit 201 or the lowermost primary transfer unit 203. This makes it possible to transfer the special color toner in the required order (details will be described later).

[0033] In the direction of travel of the intermediate transfer belt 2, a driven roller 21A acting as a second tensioning roller and a detection sensor 22 acting as a detection mechanism are provided between the primary transfer roller 7C and the primary transfer roller 7T. The driven roller 21A tensions the intermediate transfer belt 2. The detection sensor 22 detects the scale on the intermediate transfer belt 2 and detects the travel speed of the intermediate transfer belt 2. By controlling the speed of the intermediate transfer belt 2 based on this detection result, misalignment of the toner images of each color transferred to the intermediate transfer belt 2 can be suppressed.

[0034] In the transfer apparatus 20 of this embodiment, each primary transfer roller 7 contacts or separates from the photoreceptor 3 via the intermediate transfer belt 2, according to the mode during image formation. Specifically, as shown in modes A to F in Table 1 below, each primary transfer roller 7 can change its position between a contact position in which it contacts the photoreceptor 3 via the intermediate transfer belt 2 to form a primary transfer nip, and a separated position in which it is separated from the photoreceptor 3. In addition, the driven roller 21A that tensions the intermediate transfer belt 2 and the driven roller 33A as the first tensioning roller move in the downward direction in Figure 2, which is the direction away from the photoreceptor 3, or upward, which is the opposite direction, in conjunction with the primary transfer roller 7T of the downstream primary transfer section 203. The primary transfer roller 7T of the downstream primary transfer section 203 can change its position between a contact position in which it contacts the photoreceptor 3 to form a primary transfer nip, a small separated position with a small distance from the photoreceptor 3, and a large separated position with a large distance from the photoreceptor 3. In conjunction with the primary transfer roller 7T, the driven rollers 21A and 33A also move either upward in Figure 2, which is towards the photoreceptor 3, or downward in Figure 2, which is away from the photoreceptor 3. Note that Figure 2 shows the case of mode D, in which all primary transfer rollers 7 are in contact with the intermediate transfer belt 2. [Table 1]

[0035] Figures 3(a) to 3(f) show the transfer apparatus 20 for each of the A to F modes. In the separated position of each mode, each primary transfer roller 7 is moved downward in Figure 3, thereby separating the primary transfer roller 7 from the photoreceptor 3. As a result, the tension position of the intermediate transfer belt 2, which is stretched by each roller, changes in the direction of the double arrow B, which is the vertical direction as shown in Figure 2. This double arrow B direction is the direction in which the intermediate transfer belt 2 moves toward and toward each photoreceptor 3, and is also the direction in which each primary transfer roller 7 moves toward and toward the photoreceptor 3. In addition, the driven rollers 21A and 33A move downward in Figure 3 in conjunction with the separation movement of the downstream primary transfer roller 7T from the photoreceptor 3T, and the driven rollers 21A and 33A move upward in Figure 3 in conjunction with the approach movement of the primary transfer roller 7T from the photoreceptor 3T. The detection sensor 22 also moves downward in Figure 3 as the primary transfer roller 7T moves from the contact position or from the large separation position to the small separation position. The operation of the primary transfer rollers and other components in each of these modes will be described later. Also, in Table 1, the position of the driven roller 33A in the "contact" state is the first position, the position of the driven roller 33A in the "small separation" state is the second position, and the position of the driven roller 33A in the "large separation" state is the third position. Note that each roller does not move strictly in the upward or downward direction shown in Figure 3.

[0036] Figure 4 shows the switching between each mode. The area enclosed by the solid line in Figure 4 shows the switching when black toner is placed in the downstream primary transfer section 203, and the area enclosed by the dotted line in Figure 4 shows the switching when a special color toner is placed in the downstream primary transfer section 203. In other words, Mode C is a mode used only when black toner is placed in the downstream primary transfer section 203, and Mode E is a mode used when a special color toner is placed in the downstream primary transfer section 203, and there is no switching between Mode C and Mode E.

[0037] By changing these modes, only the primary transfer sections necessary for image formation can form primary transfer nips. Therefore, it is possible to prevent the formation of primary transfer nips in primary transfer sections that are not necessary for image formation, thus preventing the consumption of excess toner. For example, when forming a monochrome image on a recording sheet, mode F causes only the uppermost primary transfer section 201 to form a black transfer nip NK. In particular, in a transfer device configured to allow for both transferring special color toner at the uppermost primary transfer section 201 and transferring special color toner at the lowermost primary transfer section 203, as in this embodiment, by providing the primary transfer rollers 7 of the uppermost primary transfer section 201 and the lowermost primary transfer section 203 to be able to contact and separate from the photoreceptor 3, the primary transfer rollers 7 in the special color primary transfer section can be separated from the photoreceptor 3 as needed, regardless of the position at which the special color toner is transferred. Therefore, the consumption of excess special color toner can be suppressed in any mode.

[0038] Furthermore, when each primary transfer roller 7 of the central primary transfer unit 202 is positioned in contact with the other primary transfer roller 7T of the downstream primary transfer section 203 is positioned in a separated position, as shown in mode E, the driven roller 33A that tensions the intermediate transfer belt 2 is moved significantly in the direction away from the photoreceptor 3 by setting it to a "large separation" state. This makes it possible to change the position on which the intermediate transfer belt 2 is tensioned to a position further away from the photoreceptor 3. This prevents interference between the photoreceptor 3T and the intermediate transfer belt 2, and prevents damage to the photoreceptor 3T and the intermediate transfer belt 2 caused by this interference.

[0039] Furthermore, during the switching between modes, the order in which each component is brought into contact with or separated from is predetermined for some switching phases. Specifically, in the case of mode A→E, the primary transfer roller 7T and driven rollers 21A and 33A are first set to a "large separation" state, and then each primary transfer roller 7 of the central primary transfer unit 202 is set to a "contact" state. Conversely, in the case of mode E→A, each primary transfer roller 7 of the central primary transfer unit 202 is first set to a "separated" state, and then the primary transfer roller 7T and driven rollers 21A and 33A are set to a "small separation" state. In these cases, the timing of switching between the "separated" and "contact" states of the primary transfer roller 7K of the uppermost primary transfer section 201 is arbitrary. In the case of mode B→F, the primary transfer roller 7T and driven rollers 21A and 33A are first set to a "small separation" state, and then the primary transfer roller 7K of the uppermost primary transfer section 201 is set to a "contact" state. Conversely, in mode F→B, the primary transfer roller 7K of the uppermost primary transfer section 201 is moved to a "separated" state, and then the primary transfer roller 7T and the driven rollers 21A and 33A are moved to a "contact" state. In mode E→F, each primary transfer roller 7 of the central primary transfer unit 202 is moved to a "separated" state, and then the primary transfer roller 7T and the driven rollers 21A and 33A are moved to a "small separation" state. Conversely, in mode F→E, the primary transfer roller 7T and the driven rollers 21A and 33A are moved to a "large separation" state, and then the primary transfer roller 7 of the central primary transfer unit 202 are moved to a "contact" state. In this way, by moving the separated side first, damage to both the intermediate transfer belt 2 and the photoreceptor 3 due to contact can be suppressed.

[0040] In this embodiment, as will be described later, the primary transfer roller 7T and the driven rollers 21A and 33A move simultaneously by a common movement mechanism. However, if they move by different movement mechanisms, the order of their movement is arbitrary.

[0041] Next, the first contact / separation mechanism (first moving mechanism) that moves the primary transfer roller 7T, located in the downstream primary transfer section 203, toward and toward the intermediate transfer belt 2 will be described. First, the motor, which is the drive source for the first contact / separation mechanism, and the configuration of its surroundings will be described using Figures 5 and 6. Figure 5 is a perspective view of the area around the motor 23, and Figure 6 is a perspective view of Figure 5 with the bracket 29 covering the gear train removed.

[0042] As shown in Figures 5 and 6, a stepping motor, motor 23, is connected to a two-stage gear 24. The two-stage gear 24 meshes with the motor 23 at one tooth, and the output of the motor 23 causes the two-stage gear 24 to rotate. The other tooth of the two-stage gear 24 meshes with the teeth provided on the shaft of pulley 25, transmitting the driving force from the motor 23 to pulley 25. A toothed belt 26 is wrapped around pulley 25 and a filler pulley 27. The teeth on the inner surface of the toothed belt 26 mesh with the teeth on the outer surfaces of pulley 25 and filler pulley 27.

[0043] The driving force of the motor 23 rotates a cam that moves the primary transfer roller 7T (described later) into and out of contact with it, and is also transmitted to the filler pulley 27 via the two-stage gear 24, pulley 25, and toothed belt 26, causing the filler pulley 27 to rotate.

[0044] A photosensor 28 is provided opposite the filler pulley 27. By rotating the filler pulley 27, it is possible to change whether or not the filler 27a provided on the filler pulley 27 is positioned opposite the photosensor 28, thereby changing the detection state of the photosensor 28. The photosensor 28 is mounted on a bracket 29.

[0045] Figure 5 shows the case where the primary transfer roller 7T is positioned at a small separation position, Figure 7 shows the contact position, and Figure 8 shows the large separation position. From the large separation position in Figure 8, where the filler 27a faces the photosensor 28, the motor 23 is driven for a predetermined number of pulses to rotate the filler 27a counterclockwise, and then the motor 23 is stopped and excited to switch to the small separation position. Then, from the position in Figure 8, the motor 23 is driven for a predetermined number of pulses to rotate the filler 27a clockwise, and then the motor 23 is stopped and excited to switch to the small separation position in Figure 7. In other words, the switching to the contact position and the small separation position is done via the large separation position. The driving force of this single motor 23 switches the primary transfer roller 7T, the driven rollers 21A and 33A, and the detection sensor 22 between three positions.

[0046] Next, the first contact / separation mechanism 91, which operates the primary transfer roller 7T and the driven rollers 21A and 33A using the driving force of the motor 23, will be explained with reference to Figure 9. Figure 9 is a cross-sectional view of the image forming apparatus taken from the rear side, which is the opposite side from Figure 1, etc.

[0047] As shown in Figure 9, the first contact / separation mechanism 91 is provided with a cam member 31 that transmits the driving force of the motor 23. The cam member 31 has a first cam 31A (see Figure 12) and a second cam 31B, and is rotatably mounted around the rotation shaft 31a. The second cam 31B is a ball bearing with an outer ring and is an eccentric cam with respect to the rotation shaft 31a.

[0048] The first cam 31A contacts the front slider 32, which acts as a sliding member. As shown in Figure 9, the front slider 32 is biased to the left in Figure 9 by a spring. The driving force of the motor 23 causes the first cam 31A to rotate, changing the surface that contacts the front slider 32, thereby moving the front slider 32 to the right in Figure 9 against the biasing force of the spring.

[0049] A driven roller 33A, which is one of the rollers that tensions the intermediate transfer belt 2, is provided at one end of the rotating member 33. The rotating member 33 is rotatable around a pivot point 33a. The rotating member 33 has a hole 33b at the end opposite to the side on which the driven roller 33A is provided. An insertion part 32a provided on the front slider 32 is inserted into the hole 33b. The insertion part 32a is constructed by press-fitting a ball bearing into a shaft fixed to the front slider 32. By providing a ball bearing in the insertion part 32a, the sliding resistance between the insertion part 32a and the rotating member 33 can be reduced. A primary transfer roller 7T is provided at one end of the rotating member 34. The rotating member 34 is rotatable around a pivot point 34a. The rotating member 34 has a hole 34b at the end opposite to the side on which the primary transfer roller 7T is provided. A pin 32b provided on the front slider 32 is inserted into the hole 34b. The spring 35 is fixed to the housing of the image forming apparatus and biases the rotating member 34 to rotate clockwise around the pivot point 34a as shown in Figure 9. The driven roller 33A is the first tension roller provided downstream of the primary transfer roller 7T of the downstream primary transfer section 203.

[0050] As the front slider 32 moves left to right in Figure 9, the insertion part 32a pushes the rotating member 33, causing the rotating member 33 to rotate around the pivot point 33a. This changes the position of the driven roller 33A. Alternatively, as the front slider 32 moves right in Figure 9, the rotating member 34 is pushed by the pin 32b and rotates counterclockwise around the pivot point 34a against the biasing force of the spring 35. Or, as the front slider 32 moves left in the figure, the biasing force of the spring 35 causes the rotating member 34 to rotate clockwise around the pivot point 34a. These movements cause the primary transfer roller 7T on the rotating member 34 to move toward and away from the photoreceptor 3.

[0051] As shown in Figure 9, upstream of the primary transfer roller 7T in the direction of travel of the intermediate transfer belt 2, and downstream of the primary transfer roller 7C which is one step upstream of the primary transfer roller 7T, a driven roller 21A is provided that is stretched over the intermediate transfer belt 2 and is driven by the rotation of the intermediate transfer belt 2. The driven roller 21A is provided at one end of the rotating member 21. The rotating member 21 is provided so as to be rotatable about a pivot point 21a. The rotating member 21 is subjected to a force by the spring 39 that causes it to rotate clockwise about the pivot point 21a.

[0052] Figure 9 shows the transfer apparatus with the downstream primary transfer section 203 in the "contact" state. In this state, the front slider 32 is positioned furthest to the left in Figure 9 compared to the other two states. By rotating the first cam 31A (see Figure 12) to a predetermined position to a "small separation" state, the front slider 32 moves to the right of Figure 9, as shown in Figure 10. Conversely, by rotating the first cam 31A to a predetermined position to a "large separation" state, the front slider 32 moves to the right of Figures 9 and 10, as shown in Figure 11.

[0053] For example, as shown in Figure 9 → Figure 11, when the front slider 32 moves to the right in Figure 9, the rotating member 34 rotates counterclockwise around the pivot point 34a against the biasing force of the spring 35, and the primary transfer roller 7T moves away from the photoreceptor 3. In the "small separation" state in Figure 10 and the "large separation" state in Figure 11, the primary transfer roller 7T moves away from the photoreceptor 3. Also, when the front slider 32 moves to the right in Figure 9, the rotating member 33 rotates counterclockwise around the pivot point 33a, and the driven roller 33A moves to the opposite side from the intermediate transfer belt 2. In all states from Figure 9 to Figure 11, the driven roller 33A tensions the intermediate transfer belt 2, but in Figures 9 → 10 → 11, the position where the intermediate transfer belt 2 is tensioned is further away from the photoreceptor side (upper side in Figure 9, etc.). Furthermore, as the front slider 32 moves to the right in Figure 9, the pin 32c (see Figure 15) provided on the front slider 32 presses against the side of the rotating member 21 opposite to the side where the driven roller 21A is located. As a result, the rotating member 21 rotates counterclockwise around the pivot point 21a against the biasing force of the spring 39. Consequently, in Figures 10 and 11, the driven roller 21A separates from the intermediate transfer belt 2.

[0054] In this way, by changing the arrangement of the driven roller 33A in each of the "contact," "small separation," and "large separation" states, the position on which the intermediate transfer belt 2 is tensioned can be changed in each state. Therefore, the intermediate transfer belt 2 can be tensioned in an appropriate position, and the detection sensor 22 can accurately detect the running speed of the intermediate transfer belt 2. In particular, in this embodiment, the driven roller 33A is positioned downstream of the primary transfer roller 7T of the downstream primary transfer section 203, and by changing the tensioning position of the driven roller 33A that tensions the intermediate transfer belt 2 in all three states, the tensioning posture of the intermediate transfer belt 2 in each state can be appropriately changed, and the detection sensor 22 can accurately detect the running speed of the intermediate transfer belt 2. In addition, in the aforementioned mode E, which is the "large separation" state, by rotating the rotating member 33 significantly counterclockwise in Figure 11 and moving the driven roller 33A away from the photoreceptor 3T, the position on which the intermediate transfer belt 2 is tensioned can be shifted downward in Figure 11. In mode E, each primary transfer roller 7 of the central primary transfer unit 202 contacts the intermediate transfer belt 2, lifting it and positioning the intermediate transfer belt 2 closer to the photoreceptor 3T. Therefore, by shifting the position where the intermediate transfer belt 2 is stretched downwards as shown in Figure 11, damage to the photoreceptor 3T (see Figure 2) and the intermediate transfer belt 2 due to interference between the photoreceptor 3T and the intermediate transfer belt 2 can be prevented.

[0055] Next, we will describe the mechanism of the first contact / separation mechanism 91 that is used to move the detection sensor 22.

[0056] As shown in Figure 9, the outer circumferential surface of the second cam 31B, which is provided on the cam member 31, is gripped by the first arm 37, which acts as a first link member or second transmission member. The first arm 37 is rotatably mounted around a pivot point 37a. The pivot point 37a is fixed to the front slider 32 via a ball bearing. As the second cam 31B rotates, the first arm 37 rotates around the pivot point 37a, as shown in Figure 9. Also, as the front slider 32 moves due to the rotation of the first cam 31A (see Figure 12) provided on the cam member 31, the first arm 37 moves in the left-right direction in Figure 9.

[0057] Figure 12 is a perspective view showing the cam member 31. As shown in Figure 12, the cam member 31 has a first cam 31A and a second cam 31B. The cam member 31 is rotatably mounted around a rotation axis 31a. The first cam 31A has a small diameter section, a medium diameter section, and a large diameter section, each with a diameter of 120 degrees. As shown in Figure 13, the first cam 31A contacts a cam follower 36, which is made of a ball bearing. The cam follower 36 is a first transmission member provided on the first arm 37. By changing the surface that the first cam 31A contacts the cam follower 36 through rotation, the front slider 32 can be moved in the left-right direction in Figure 9. Also, as the front slider 32 moves, the first arm 37, whose pivot point 37a is fixed to the front slider 32, moves in conjunction with the front slider 32 in the left-right direction in Figure 9.

[0058] As shown in Figures 13 and 14, the first arm 37 grips the second cam 31B at two points, gripping portions 37c1 and 37c2. The rotation of the second cam 31B causes the first arm 37 to rotate around the pivot point 37a.

[0059] As shown in Figure 13, a thrust deterrent member 60, which acts as both a restricting member and a retaining member, is attached to the first arm 37. The thrust deterrent member 60 has a contact portion 60a and a restricting portion 60b, which act as retaining portions. By bringing the contact portion 60a into contact with the pivot point 37a of the first arm 37 from above in Figure 13, it functions as a retaining member for the pivot point 37a relative to the front slider 32. Figure 14 shows the thrust deterrent member 60 removed. The thrust deterrent member 60 also contacts the pivot point 37a from below in Figure 13, preventing it from coming loose downwards in Figure 13. The restricting portion 60b of the thrust deterrent member 60 is a surface provided along the outer circumferential surface of the outer ring of the second cam 31B, which is a bearing. By restricting the position of the outer circumferential surface of the second cam 31B, the relative movement direction of the first arm 37 with respect to the second cam 31B can be restricted. In other words, the first arm 37 can be restricted from moving in a direction other than along the outer circumferential surface of the second cam 31B, for example, in a sliding direction relative to the second cam 31B. Therefore, positional displacement such as tilting of the first arm 37 relative to the second cam 31B can be prevented, and wear of the gripping portions 37c1 and 37c2 can be prevented.

[0060] In this embodiment, the number of parts in the transfer device can be reduced by providing a contact portion 60a that functions as a retaining mechanism for the first arm 37 against the front slider 32, and a restricting portion 60b that restricts the relative movement direction of the first arm 37 with respect to the second cam 31B, on a common thrust stopper member 60. However, these may be provided on separate members.

[0061] Figure 15 is a front perspective view of the area around the first arm 37 and the second arm 38. Figure 16 is a rear perspective view of the first arm 37 and the second arm 38.

[0062] As shown in Figure 15, the second arm 38, which serves as the second link member, has other elongated holes 38a and 38b at both ends. One end 37b of the first arm 37 is inserted into the other elongated hole 38a. As shown in Figure 16, the one end 37b of the first arm 37 has a bearing 40. The bearing 40 is provided so as to be able to move relative to the other elongated hole 38a. The bearing 40 is the other insertion part into the other elongated hole 38a.

[0063] A parallel pin 40a is provided on the back side of the bearing 40 as a retaining part. The length of the parallel pin 40a is shorter than the length of the other slotted hole 38a in the longitudinal direction. By positioning the parallel pin 40a approximately parallel to the longitudinal direction of the other slotted hole 38a, the bearing 40 can be inserted into the other slotted hole 38a. In the three states described above—"contact," "small separation," and "large separation"—the parallel pin 40a does not rotate to a position parallel to the longitudinal direction of the other slotted hole 38a. Therefore, the parallel pin 40a functions as a retaining mechanism for the bearing 40 in the other slotted hole 38a.

[0064] As shown in Figure 15, a bearing 41 is inserted into the elongated hole 38b. The bearing 41 is fixed to the first sensor bracket 43, which acts as a retaining member, by a stepped screw 42. The bearing 41 is provided to be movable within the elongated hole 38b. The bearing 41 is the insertion part for the elongated hole 38b.

[0065] The rotation of the cam member 31 moves the front slider 32 to the right in Figure 10 from the state in Figure 9 or Figure 10, bringing the downstream primary transfer section 203 into a "large separation" state. As a result, the rotation of the second cam 31B causes the first arm 37 to rotate clockwise around the pivot point 37a. This causes one end 37b of the first arm 37 to move downward in Figure 9 or Figure 10. As a result, as shown in Figure 11, one end 37b moves to one end of the other elongated hole 38a and contacts the wall surface forming the other elongated hole 38a, pulling the second arm 38 downward in Figure 11. This causes the bearing 41 to move relative to one end of the elongated hole 38b and contact the wall surface forming the elongated hole 38b. Then, the second arm 38 pulls the first sensor bracket 43 downward in Figure 11.

[0066] Figure 17 shows the configuration around the first sensor bracket 43 and the detection sensor 22, and is a diagram showing the state with the rotating member 21 removed from Figure 9 and other figures. For convenience, the detection sensor 22 and the second sensor bracket 44 are shown in a simplified manner in Figure 17.

[0067] As shown in Figure 17, the first sensor bracket 43 is rotatably mounted around a pivot point 43a. The first sensor bracket 43 is subjected to a force by a spring 45 fixed to the housing of the image forming apparatus, which causes it to rotate counterclockwise around the pivot point 43a as shown in Figure 17. A regulating member 63 is also fixed to the first sensor bracket 43. The pin 32d of the front slider 32 is inserted into the hole 63a of the regulating member 63. In the "contact" state in Figure 9 and the "small separation" state in Figure 10, the pin 32d contacts the wall surface forming the hole 63a, causing the front slider 32 to apply a force to the first sensor bracket 43 that causes it to rotate clockwise around the pivot point 43a as shown in Figure 17.

[0068] The second sensor bracket 44 is fixed to the first sensor bracket 43 via a stud 43b provided on the first sensor bracket 43. The second sensor bracket 44 holds the detection sensor 22. The second sensor bracket 44 has a hook 44a to which one end of a spring 62 (see Figure 9) is attached, a first contact portion 44b, and a second contact portion 44c.

[0069] In the "contact" state shown in Figure 9, the second sensor bracket 44 is biased by the spring 62 and moves in a direction that rotates clockwise around the pivot point 43a, and is positioned so that the first contact portion 44b contacts the stud 64 provided on the housing of the image forming apparatus.

[0070] On the other hand, in the "small separation" state shown in Figure 10, the pin 32d provided on the front slider 32 moves to the right of the position shown in Figure 9, causing the first sensor bracket 43, the second sensor bracket 44, and the detection sensor 22 to rotate counterclockwise around the pivot point 43a due to their own weight and the biasing force of the spring 45. Also, the pin 43c provided on the first sensor bracket 43, shown in Figure 18, presses against the bent portion 44d of the second sensor bracket 44, causing the second sensor bracket 44 to rotate counterclockwise around the pivot point 43a as shown in Figure 10. As a result, the first sensor bracket 43, the second sensor bracket 44, and the detection sensor 22 rotate counterclockwise as shown in Figure 10, moving downward in Figure 10, which is further away from the photoreceptor 3 than in Figure 9. Figure 18 is a perspective view showing the back side of the paper shown in Figure 10 for the first sensor bracket 43 and the second sensor bracket 44.

[0071] Furthermore, in the "large separation" state shown in Figure 11, as the pin 32d moves further to the right, the force with which the pin 32d presses the restricting member 63 to the left in Figure 17 is released, as shown in Figure 17. Simultaneously, as described above, the second arm 38 pulls the first sensor bracket 43 towards the lower left of Figure 17, causing the first sensor bracket 43 to rotate clockwise in Figure 17 around the pivot point 43a. As a result, the second sensor bracket 44, which is fixed to the first sensor bracket 43 via the stud 43b, moves upward in Figure 17, and the detection sensor 22 also moves upward in Figure 17. At this time, as shown in Figure 19, the second sensor bracket 44 is positioned at a position where the second contact portion 44c of the second sensor bracket 44 contacts the positioning portion 21b of the rotating member 21. In other words, the upward movement of the second sensor bracket 44 and the detection sensor 22 in Figure 17 is restricted, and the detection sensor 22 is positioned. In this embodiment, the positioning location is lower than the "contact" state in Figure 9 and higher than the "small separation" state in Figure 10.

[0072] In this way, by transmitting the driving force of the cam member 31 to the first sensor bracket 43 via link members such as the first arm 37 and the second arm 38, and by creating a mechanism that rotates the first sensor bracket 43, the first sensor bracket 43 can be rotated in a desired direction.

[0073] In particular, in this embodiment, by providing a mechanism in which the rotational force of the first arm 37 is transmitted to the second arm 38 only under predetermined conditions, the driving force due to the rotation of the cam member 31 can be transmitted to the detection sensor 22 only when a specific position change occurs. Specifically, by configuring the second arm 38 to be connected to the first arm 37 or the first sensor bracket 43 via other elongated holes 38a and 38b provided in the second arm 38, the second arm 38 can be retracted only when the "large separation" state is reached, moving the detection sensor 22 downwards as shown in Figure 11. In other words, compared to the primary transfer roller 7T and driven rollers 21A and 33A, which move in a constant direction in conjunction with the movement of the front slider 32, the detection sensor 22 moves upwards as shown in Figure 10 when the transition is "contact" → "small separation", while it moves downwards as shown in Figure 11 when the transition is "contact" → "large separation" or "small separation" → "large separation", thus moving in the opposite direction to the movement of the front slider 32. In the "small separation" state, the primary transfer rollers of the uppermost primary transfer section 201 and the central primary transfer unit 202 separate from the photoreceptor 3, causing the position where the intermediate transfer belt 2 is tensioned to move downward in Figure 10. On the other hand, in the "large separation" state, the primary transfer rollers of the central primary transfer unit 202 contact the photoreceptor 3 via the intermediate transfer belt 2, pushing the intermediate transfer belt 2 upward in Figure 11. Therefore, by changing the arrangement of the detection sensor 22 as described above, the detection sensor 22 can be positioned according to the tensioned position of each intermediate transfer belt 2. Thus, the detection accuracy of the detection sensor 22 for the intermediate transfer belt 2 can be improved in each mode, and the running speed of the intermediate transfer belt 2 can be controlled with precision. Furthermore, the first contact / separation mechanism 91 can control the operation of the detection sensor 22 and the operation of the primary transfer rollers 7T, driven rollers 21A, and 33A using the driving force of a single drive source, the motor 23. Thus, energy saving and a reduction in the number of parts of the transfer device can be achieved.

[0074] However, the number of link members connected to the first sensor bracket 43 that holds the detection sensor 22 is not limited to two in this embodiment. There may be three or more, or just one. Also, the combination of members providing elongated holes and insertion members such as pins inserted into them may be reversed. Furthermore, it is not necessarily required that the detection sensor 22, primary transfer roller 7T, driven rollers 21A and 33A be operated by the driving force of the motor 23.

[0075] As described above, in this embodiment, the rotation of the first cam 31A shown in Figure 12 moves the front slider 32 in the left-right direction in Figure 9, thereby moving each primary transfer roller 7 and the driven roller. Furthermore, the rotation of the first cam 31A and the second cam 31B moves the detection sensor 22. Specifically, in the "contact" state in Figure 9 and the "small separation" state in Figure 10, the rotation of the first cam 31A applies pressure by the pin 32d (see Figure 16), which moves, to the first sensor bracket 43, applying a force in a clockwise direction, thereby changing the position of the detection sensor 22. In the "large separation" state, the rotation of the second cam 31B pulls the first sensor bracket 43 into the second arm 38, thereby changing the position of the detection sensor 22.

[0076] Next, the second contact / separation mechanism 92, which acts as a second moving mechanism to bring the primary transfer rollers 7C, 7M, and 7Y provided in the central primary transfer unit 202 into contact with and separate from the intermediate transfer belt 2, and the third contact / separation mechanism 93, which acts as a third moving mechanism to bring the primary transfer roller 7K provided in the uppermost primary transfer section 201 into contact with and separate from the intermediate transfer belt 2, will be explained with reference to Figure 20.

[0077] As shown in Figure 20, the second contact / disconnection mechanism 92 includes rotating members 46-48, a cam 51, and a cam follower 52. The third contact / disconnection mechanism 93 includes a rotating member 49, a cam 53, and a cam follower 54. The second contact / disconnection mechanism 92 is equipped with a motor as a drive source for rotating the cam 51, and the third contact / disconnection mechanism 93 is equipped with a motor as a drive source for rotating the cam 53.

[0078] Rotating members 46, 47, 48, and 49 are rotatably mounted around pivot points 46a, 47a, 48a, and 49a. A primary transfer roller 7C is provided at one end of rotating member 46. A primary transfer roller 7M is provided at one end of rotating member 47. A primary transfer roller 7Y is provided at one end of rotating member 48. A primary transfer roller 7K is provided at one end of rotating member 49. Each of the rotating members 46 to 49 is biased by a spring to rotate in the clockwise direction shown in Figure 20, and each primary transfer roller 7 is brought into contact with the photoreceptor via the intermediate transfer belt 2.

[0079] The rotation of the cam 51 causes the cam follower 52 to rotate, moving the front slider 50 of the uppermost primary transfer section 201 to the right in Figure 20. This presses the ends of the rotating members 46-48 opposite to the side on which the primary transfer rollers 7 are installed, causing each rotating member 46-48 to rotate counterclockwise in Figure 20 against the biasing force of the spring. As a result, each primary transfer roller 7C, 7M, and 7Y separates from the intermediate transfer belt 2. The rotation of the cam 53 also causes the cam follower 54 to rotate, pressing the end of the rotating member 49 opposite to the side on which the primary transfer roller 7K is installed. As a result, the rotating member 49 rotates counterclockwise in Figure 20 against the biasing force of the spring, causing the primary transfer roller 7K to separate from the intermediate transfer belt 2. As described above, the primary transfer roller 7K of the uppermost primary transfer section 201 and the primary transfer rollers 7C, 7M, and 7Y of the central primary transfer unit 202 independently perform contact and separation movements with respect to the intermediate transfer belt 2.

[0080] Next, the toner replenishment device for supplying toner to the developing unit will be explained using Figures 21 to 23.

[0081] As shown in Figure 21, the image forming apparatus 1 has a bottle storage section 101 at the top of its housing. Toner bottles 102Y, 102M, 102C, 102K, and 102T, which contain replenishment Y toner, M toner, C toner, K toner, and special color toner, are mounted in this bottle storage section 101. Additionally, bottle drive units 103Y, 103M, 103C, 103K, and 103T (see Figure 23) for the toner replenishment device are fixed to this section. Each bottle drive unit detachably holds each toner bottle.

[0082] Figure 23 is a schematic diagram showing the toner bottle, toner replenishment device, developing device, and photoreceptor for one of the following colors: T, Y, M, C, and K. For convenience, the subscripts T, Y, M, C, and K attached to the symbols are omitted in this figure.

[0083] The toner replenishment device 150 includes a bottle drive unit 103, a pre-replenishment storage unit 104, a toner replenishment member 105, a suction pump 106, and a transfer tube 107. The pre-replenishment storage unit 104 is located directly above the developing device 6. The transfer tube 107 has one end connected to the bottle drive unit 103 and the other end connected to the suction pump 106, forming a toner transport path that transports toner from the bottle drive unit 103 to the pre-replenishment storage unit 104. In this embodiment, the transfer tube 107 is made of a flexible tube.

[0084] The bottle drive unit 103 rotates the toner bottle 102, transferring the toner contained in the toner bottle 102 from the top opening of the toner bottle 102 to the bottle drive unit 103. The suction pump 106, through its suction action, transfers the toner in the bottle drive unit 103 to the suction pump 106 via the transfer tube 107, and also drops the toner sucked from the bottle drive unit 103 into the pre-replenishment storage unit 104 from the outlet of the suction pump 106.

[0085] Then, due to the rotation of the toner supply member 105, the toner stored in the pre-supply storage unit 104 is supplied to the developing device 6 via the toner supply passage 108. In this embodiment, the toner transferred from the bottle drive unit 103 to near the developing device 6 by the suction pump 106 is temporarily stored in the pre-supply storage unit 104.

[0086] Incidentally, for example, when using white toner as a special color to create a white background in an image, it is necessary to form a white toner layer at the bottom of the image, and the downstream primary transfer unit 203 must be placed at the downstream end of the primary transfer unit. On the other hand, when transferring a transparent toner image to give an image glossiness, a transparent toner image is formed on the surface of the image. Therefore, in this case, the downstream primary transfer unit 203 must be placed at the upstream end of the primary transfer unit.

[0087] Thus, because the order in which special colors are transferred must be changed depending on the type of special color used, in this embodiment, the toner supplied to the uppermost primary transfer unit 201 and the lowermost primary transfer unit 203 can be changed as shown in Figures 21 and 22. Specifically, in Figure 21, the special color toner bottle 102T is connected to the lowermost pre-supply storage unit 104T on the right side of Figure 21, and the black toner bottle 102K is connected to the uppermost pre-supply storage unit 104K. In Figure 22, the black toner bottle 102K is connected to the lowermost pre-supply storage unit 104K on the right side, and the special color toner bottle 102T is connected to the uppermost pre-supply storage unit 104T in Figure 22. Furthermore, in Figures 21 and 22, the arrangement of the toner bottles 102K and 102T, and the transfer tubes 107K and 107T connected to the toner bottles 102K and 102T remain unchanged, but the destination to which the transfer tubes 107K and 107T are connected is changed. In other words, in Figure 21, the transfer tube 107K is extended and connected to the upstream suction pump 106T. On the other hand, in Figure 22, the transfer tube 107K is connected to the downstream suction pump 106T. Unlike the transfer tube 107T, the transfer tube 107K is extended significantly upstream in Figure 22. This allows the transfer position where black and special color toners are first transferred to be changed simply by replacing the pre-replenishment storage unit 104 and the image forming unit 10, without having to replace the toner bottle or bottle drive unit, thereby reducing the effort required for replacement work. Note that the actual lengths of the transfer tubes 107T in Figure 21 and 107K in Figure 22 are longer than shown, and space is provided within the image forming apparatus to accommodate the excess tubes.

[0088] Next, the process of changing the color of the toner transferred in these primary transfer sections will be explained using the flowchart in Figure 24.

[0089] As shown in Figure 24, first, the toner color arrangement is changed (step S1). Specifically, black is placed in the uppermost primary transfer section and special colors in the lowermost primary transfer section, or conversely, special colors are placed in the uppermost primary transfer section and black is placed in the lowermost primary transfer section. The control unit of the image forming apparatus then determines whether each color is correctly arranged, and if not, displays a message prompting replacement on the operation display unit (steps S2, S3). The operator then turns off the power to the image forming apparatus, replaces the pre-replenishment storage unit and the image forming unit, and then turns the power to the image forming apparatus back on (steps S4-S6). The image forming apparatus then determines again whether the replacement has been done correctly (step S7), and if not, displays a message on the operation display unit again (step S8).

[0090] Steps S2 and S7 determine whether the black and special colors are correctly positioned, and also determine whether the correct colors are set, such as whether the special color is transparent or white.

[0091] Alternatively, before changing the settings of the image forming apparatus, the procedure may be to turn off the power as in step S4 and change the toner color arrangement as in step S5.

[0092] As shown in Figure 25, a control unit 300 provided in the image forming apparatus determines whether the black and special colors in steps S1 and S6 are correctly positioned. The control unit 300 has a determination circuit 301 that determines the mounting status of the pre-replenishment storage unit 104 and the image forming unit 10.

[0093] The determination circuit 301 includes a first connector 302 connected to the pre-replenishment storage unit located at the uppermost position, a second connector 303 connected to the pre-replenishment storage unit located at the lowermost position, a third connector 304 connected to the image-making unit located at the uppermost position, and a fourth connector 305 connected to the image-making unit located at the lowermost position. Furthermore, the pre-replenishment storage unit 104K is provided with a circuit board 104K1 connected to the above connectors, and the pre-replenishment storage unit 104T is provided with a circuit board 104T1 connected to the above connectors. The circuit board 10K1 connected to the above connectors is provided, for example, in the developing container of the developing device of the image-making unit 10K, and the circuit board 10T1 connected to the above connectors is provided, for example, in the developing container of the developing device of the image-making unit 10T.

[0094] Each connector 302-305 is provided with multiple switches. Based on the combination of ON / OFF states of the switches when each circuit board is connected to each connector, the determination circuit 301 can determine whether a black or special color board is installed, and if a special color board is installed, which special color it is. If it is not necessary to determine which special color board is installed, and only whether it is black or a special color board, the determination can be made by the ON / OFF states of the filler and the photosensor.

[0095] The control unit 300 also receives the detection result from the detection sensor 22. Based on this detection result, the control unit 300 changes the travel speed of the intermediate transfer belt 2.

[0096] Next, modified versions of the transfer apparatus described above will be explained using Figures 26 and 27. Figure 27(a) shows the "contact" state in which each primary transfer roller 7C, 7M, and 7Y are in contact with the intermediate transfer belt 2, and Figure 27(b) shows the "separated" state.

[0097] As shown in Figure 26, in this embodiment, a driven roller 55A is provided between the primary transfer roller 7T, which is located in the downstream primary transfer section 203, and the primary transfer roller 7C upstream of it, for tensioning the intermediate transfer belt 2. The driven roller 55A is located upstream of the detection sensor 22. As shown in Figure 27(a), the driven roller 55A is located at one end of the rotating member 55. The rotating member 55 is rotatable around a pivot point 55a located at the end opposite to the side with the driven roller 55A.

[0098] The second contact / separation mechanism 92 has a cam 51. The pivot point 55a is fixed to the front slider 50 that brings the primary transfer rollers 7C, 7M, and 7Y of the central primary transfer unit 202 into contact with and separate from each other. When the front slider 50 moves to the right in Figure 27 due to the rotation of the cam 51, the rotating member 55 rotates clockwise around the pivot point 55a as shown in Figure 27(b).

[0099] In this embodiment, the driven roller 55A contacts the intermediate transfer belt 2 in a "contact" state with the central primary transfer unit 202, thereby tensioning the intermediate transfer belt 2. In the aforementioned mode E, where the downstream primary transfer section 203 is "largely separated" and the central primary transfer unit 202 is "contacting" the intermediate transfer belt 2, the downstream primary transfer roller 7T is separated from the photoreceptor 3, which tends to reduce the nip pressure of each transfer nip of each primary transfer roller 7 of the central primary transfer unit 202. In contrast, by placing the driven roller 55A between the downstream primary transfer roller 7T and the primary transfer roller 7C immediately upstream of it, and bringing it into contact with the intermediate transfer belt 2 in a "contact" state with the central primary transfer unit 202, a decrease in transfer pressure in the central primary transfer unit 202 can be prevented.

[0100] Furthermore, by providing the detection sensor 22 between the driven roller 55A and the primary transfer roller 7T, the running speed of the intermediate transfer belt 2 can be detected without being affected by the vibration of the driven roller 55A, thus particularly improving the accuracy of the running speed of the intermediate transfer belt 2 in the downstream primary transfer section 203.

[0101] Next, an embodiment in which a driven roller 56A, positioned between the downstream primary transfer roller 7T and the upstream primary transfer roller 7C, is moved by a first contact / separation mechanism that brings the downstream primary transfer roller into contact with and separates from it, will be described using Figure 28. Figure 28(a) shows the "contact" state, Figure 28(b) shows the "small separation" state, and Figure 28(c) shows the "large separation" state.

[0102] As shown in Figure 28(a), the rotating member 56 is rotatably mounted around a pivot point 56a located at the end opposite to the side with the driven roller 56A. The pivot point 56a is fixed to the front slider 32 that moves the primary transfer roller 7T of the downstream primary transfer section 203 toward and toward. The mechanism for moving the detection sensor 22 toward and toward is the same as in the previously described embodiment, so its description is omitted.

[0103] A hole 56b is provided in the rotating member 56. The pin 32e of the front slider 32 is inserted into the hole 56b. The hole 56d is provided so that the height of both ends in the left-right direction of Figure 28, which is the direction of movement of the front slider 32 (the height in the up-down direction of Figure 28, and the height in the direction of contact with and separation from the intermediate transfer belt 2) is the same, and it has a shape in which a convex portion 56b1 protrudes toward the intermediate transfer belt 2 at the center in the left-right direction of Figure 28, which is the direction of movement of the front slider 32. With this shape, the driven roller 56A is separated from the intermediate transfer belt 2 only when the downstream primary transfer section 203 is in a "small separation" state, and the driven roller 56A is brought into contact with the intermediate transfer belt 2 when it is in a "large separation" state. In other words, when the downstream primary transfer section 203 in Figure 28(b) is in a "small separation" state, the pin 32e of the front slider 32 fits into the protrusion 56b1 of the hole 56b, causing the rotating member 56 to rotate clockwise in Figure 28. This causes the driven roller 56A to separate from the intermediate transfer belt 2. On the other hand, when the separation is large, the pin 32e moves to the right end of the hole 56d, causing the rotating member 56 to rotate counterclockwise, and the driven roller 56A comes into contact with the intermediate transfer belt 2.

[0104] In this embodiment as well, the driven roller 56A can be brought into contact with the intermediate transfer belt 2 when the downstream primary transfer section 203, which is in a "contact" state with the central primary transfer unit 202, is in a "large separation" state. This prevents a decrease in the transfer pressure in the central primary transfer unit 202. Furthermore, due to the shape of the aforementioned hole 56d, the driven roller 56A can be separated from the intermediate transfer belt 2 only when the downstream primary transfer section 203 is in a "small separation" state.

[0105] Furthermore, the downstream primary transfer unit 203 can be configured to switch between only two positions, "contact" and "large separation," as in the embodiment described above. However, in this case, a combination will occur where the downstream primary transfer unit 203 is "large separation" and the central primary transfer unit 202 is "separated," requiring a configuration to adjust the excess belt length of the intermediate transfer belt 2.

[0106] Figure 29 shows the state of Mode D described above, in which the downstream primary transfer section 203 and the central primary transfer unit 202 are in "contact" with each other.

[0107] In Figure 29, each primary transfer roller 7 and driven roller contacts the intermediate transfer belt 2 from below in Figure 29, thereby tensioning the intermediate transfer belt 2. From this state, the downstream primary transfer section 203 is moved to a "large separation" state and the central primary transfer unit 202 is moved to a "separated" state. In other words, each primary transfer roller 7Y, 7M, 7C, 7T and driven roller 33A are moved downwards in Figure 29, separating the intermediate transfer belt 2 from each photoreceptor 3Y, 3M, 3C, 3T. As a result, the difference in circumference of the intermediate transfer belt 2 becomes larger compared to the case in Figure 29, and excess material is created in the intermediate transfer belt 2.

[0108] Therefore, in this embodiment, the intermediate transfer belt 2 is provided with a variable mechanism that allows the position of the tension roller 65 to be varied. The tension roller 65 applies tension from the outer circumferential surface side of the intermediate transfer belt 2. This variable mechanism will be explained using Figures 30(a) and 30(b). Figure 30(a) shows the state of mode D, in which the downstream primary transfer section 203 and the central primary transfer unit 202 are in "contact," and Figure 30(b) shows the state in which the downstream primary transfer section 203 is "largely separated" and the central primary transfer unit 202 is "separated." The other mechanisms are the same as in the embodiment described above.

[0109] As shown in Figure 30(a), the tension roller 65 is attached to one end of the rotating mechanism 66. The rotating mechanism 66 is rotatable around a pivot point 66a. One end of a spring 67 is fixed to the other end of the rotating mechanism 66. The other end of the spring 67 is fixed to the housing of the image forming apparatus by a stud 68. The spring 67 applies a force to the rotating mechanism 66 in a counterclockwise direction around the pivot point 66a as shown in Figure 30(a).

[0110] For example, when the central primary transfer unit 202 and the downstream primary transfer section 203 in Figure 29 are changed from a "contacting" state to a "separated (or greatly separated)" state, the tensioning position of the intermediate transfer belt 2 is lower than in Figure 29, and the circumference of the intermediate transfer belt 2 on the primary transfer side becomes shorter. At this time, as shown in Figure 30(a) → Figure 30(b), the rotation mechanism 66 rotates further counterclockwise around the pivot point 66a due to the tensile force of the spring 67, and the position in which the tension roller 65 is pressed against the intermediate transfer belt 2 changes. In other words, the tension roller 65 is pressed against the intermediate transfer belt 2 by the spring 67. This makes it possible to absorb the excess circumference of the intermediate transfer belt 2 on the primary transfer side.

[0111] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the present invention.

[0112] Recording sheets include not only plain paper (Paper P), but also cardboard, postcards, envelopes, thin paper, coated paper (such as coated paper and art paper), tracing paper, OHP sheets, plastic film, prepreg, copper foil, etc.

[0113] In the above embodiment, the primary transfer roller 7T and driven rollers 33A and 21A of the downstream primary transfer section 203 are shown to be moved by a driving force from a common drive source, but they may also be moved by driving forces from separate drive sources.

[0114] In the embodiments described above, the case was shown in which the distance of the primary transfer roller 7T, which is the downstream primary transfer member, from the photoreceptor 3 is increased when the separation is large compared to when the separation is small. However, the primary transfer roller 7T may not move in either the small or large separation states.

[0115] The above description shows a configuration in which the primary transfer rollers of all primary transfer sections make contact with and separate from the photoreceptor. However, it is sufficient if at least the primary transfer rollers of the downstream primary transfer section and one of the primary transfer sections upstream of it make contact with and separate from the photoreceptor. Furthermore, it is not necessarily required to be a transfer device that transfers five colors of toner, including a special color.

[0116] Examples of the present invention are as follows: <1> An intermediate transfer unit that travels in a circular motion, A plurality of primary transfer sections, each having a primary transfer member, transfer a developer image to the intermediate transfer body, Among the primary transfer sections, a first tension roller is positioned downstream of the downstream primary transfer member, which is the primary transfer member of the downstream primary transfer section located furthest downstream in the direction of travel of the intermediate transfer body, and tensions the intermediate transfer body. A first moving mechanism moves the first tension roller to change the position in which the first tension roller tensions the intermediate transfer body, A transfer apparatus comprising a second moving mechanism that allows the primary transfer member of the primary transfer section, which is located upstream of the downstream primary transfer section in the direction of travel of the intermediate transfer body, to move between a contact position in which it is in contact with the latent image carrier via the intermediate transfer body and a separated position in which it is separated from the latent image carrier, The downstream primary transfer member is provided so as to be movable between a contact position in contact with the latent image carrier via the intermediate transfer body and a separated position separated from the latent image carrier. The transfer apparatus is characterized in that the first tensioning roller is moved by the first moving mechanism to at least three positions on which the intermediate transfer body is stretched. <2> Having at least five primary transfer regions, The primary transfer section further includes a third movement mechanism that allows the uppermost primary transfer member of the uppermost primary transfer section, which is located on the upstream side in the direction of travel of the intermediate transfer body, to move between a contact position in which it is in contact with the latent image carrier via the intermediate transfer body and a separated position in which it is separated from the latent image carrier. The second moving mechanism can move at least three central primary transfer members, which are primary transfer members of at least three primary transfer sections located between the uppermost primary transfer member and the lowermost primary transfer member, between a contact position where they are in contact with the latent image carrier via the intermediate transfer body and a separated position where they are separated from the latent image carrier. <1> This is the transfer device described above. <3> The downstream primary transfer member has a first contact / separation mechanism that allows it to move between the contact position and the separated position. The first tension roller is provided so as to be movable between a first position, a second position and a third position by the first moving mechanism. With the downstream primary transfer member positioned at the contact position, the first tension roller is positioned at the first position. With the downstream primary transfer member positioned at the separated position and the upstream primary transfer member positioned at the separated position, the first tension roller is positioned at the second position. With the downstream primary transfer member positioned at the separated position and the upstream primary transfer member positioned at the contact position, the first tension roller is positioned at the third position. In the direction of each primary transfer member's contact with and separation from each latent image carrier, the third position is positioned such that the first tension roller is positioned further away from the latent image carrier than the second position. <2> This is the transfer device described above. <4> The first contact / separation mechanism is the first movement mechanism. <3> This is the transfer device described above. <5> After the first moving mechanism moves the first tension roller from the second position to the third position, the second moving mechanism moves each of the central primary transfer members from the separated position to the contact position. <3> or <4> This is the transfer device described above. <6> After the second moving mechanism moves each of the central primary transfer members from the contact position to the separated position, the first moving mechanism moves the first tension roller from the third position to the second position. <3> or <4> This is the transfer device described above. <7> After the second moving mechanism moves each of the central primary transfer members from the contact position to the separated position, the first moving mechanism moves the first tension roller from the third position to the second position. <3> or <4> This is the transfer device described above. <8> After the first moving mechanism moves the first tension roller from the second position to the third position, the second moving mechanism moves each of the central primary transfer members from the separated position to the contact position. <3> or <4> This is the transfer device described above. <9> The first moving mechanism moves the first tension roller from the contact position to the second position and the downstream primary transfer member from the contact position to the separated position, after which the third moving mechanism moves the upstream primary transfer member from the separated position to the contact position. <3> or <4> This is the transfer device described above. <10> After the third moving mechanism moves the uppermost primary transfer member from the contact position to the separated position, the first moving mechanism moves the first tension roller from the second position to the contact position, and moves the lowermost primary transfer member from the separated position to the contact position. <3> or <4> This is the transfer device described above. <11> The first moving mechanism moves the downstream primary transfer member and the first tension roller using a common drive source. <3> or <4> This is the transfer device described above. <12> A second tension roller for stretching the intermediate transfer body is further provided between the downstream primary transfer section and the primary transfer section one step upstream from the downstream primary transfer section. The second tension roller tensions the intermediate transfer body while the downstream primary transfer member is separated from the intermediate transfer body, and the primary transfer member of the primary transfer section one level upstream from the downstream primary transfer section is in contact with the latent image carrier. <2> from <11> It is one of the transfer devices described above. <13> The second moving mechanism causes the second tension roller to come into contact with or separate from the intermediate transfer body. <12> This is the transfer device described above. <14> The first moving mechanism causes the second tension roller to come into contact with or separate from the intermediate transfer body. <12> This is the transfer device described above. <15> The downstream primary transfer section transfers a special color developer, which is neither yellow, magenta, cyan, nor black, to the intermediate transfer body. <1> from <14> It is one of the transfer devices described above. <16> Multiple latent image carriers, <1> from <15> An image forming apparatus comprising a transfer device as described in any of the above. [Explanation of Symbols]

[0117] 1. Image forming apparatus 2. Intermediate transfer belt (intermediate transfer body) 3. Photoreceptor (latent image carrier) 7. Primary transfer roller (primary transfer member) 20 Transfer device 21A Driven roller (second tension roller) 22 Detection Sensor (Detection Mechanism) 23. Motor (drive source) 32 Front slider (sliding part) 33A Driven roller (first tension roller) 36 Cam follower (first transmission member) 37. First arm (first link member or second transmission member) 38. Second arm (second link member) 38a Other long holes 38b long hole 40 Bearings (other insertion parts) 40a Parallel pin (retaining part) 41 Bearing (insertion part) 43. First sensor bracket (holding member) 60. Thrust stopper (regulating member or anti-loosening member) 60a Contact portion (retaining portion) 60b Regulatory Department 91 1st approach / separation mechanism (1st movement mechanism) 92 Second contact / separation mechanism (second movement mechanism) 93 Third approach / separation mechanism (third movement mechanism) 201 Uppermost primary transfer section 202 Central Primary Transfer Unit 203 Downstream primary transfer section A. Direction of travel of the intermediate transfer belt (direction of travel of the intermediate transfer body) [Prior art documents] [Patent Documents]

[0118] [Patent Document 1] Japanese Patent Publication No. 2006-30737

Claims

1. An intermediate transfer unit that travels in a circular motion, A plurality of primary transfer sections, each having a primary transfer member, transfer a developer image to the intermediate transfer body, Among the primary transfer sections, a first tension roller is positioned downstream of the downstream primary transfer member, which is the primary transfer member of the downstream primary transfer section located at the downstream end in the direction of travel of the intermediate transfer body, and tensions the intermediate transfer body. A first moving mechanism moves the first tension roller to change the position in which the first tension roller tensions the intermediate transfer body, A transfer apparatus comprising: a second movement mechanism that allows the upstream primary transfer member, which is the primary transfer member of the primary transfer section located upstream of the downstream primary transfer section in the direction of travel of the intermediate transfer body, to move between a contact position in which it is in contact with the latent image carrier via the intermediate transfer body and a separated position in which it is separated from the latent image carrier, The downstream primary transfer member is provided so as to be movable between a contact position in contact with the latent image carrier via the intermediate transfer body and a separated position separated from the latent image carrier. The first tension roller is moved by the first moving mechanism to at least three positions: a first position, a second position, and a third position on which the intermediate transfer body is tensioned. In the direction of the primary transfer member's contact with and separation from the latent image carrier, the distance of the first tension roller from the latent image carrier increases in the order of the first position, the second position, and the third position. With the downstream primary transfer member positioned in contact with the first tension roller, the first tension roller is positioned in the first position. With the downstream primary transfer member positioned at the separated position and the upstream primary transfer member positioned at the separated position, the first tension roller is positioned at the second position. A transfer device characterized in that the first tension roller is positioned at the third position when the downstream primary transfer member is positioned at the separated position and the upstream primary transfer member is positioned at the contact position.

2. Having at least five primary transfer units, The primary transfer section further includes a third movement mechanism that allows the uppermost primary transfer member of the uppermost primary transfer section, which is located on the upstream side in the direction of travel of the intermediate transfer body, to move between a contact position in which it is in contact with the latent image carrier via the intermediate transfer body and a separated position in which it is separated from the latent image carrier. The transfer apparatus according to claim 1, wherein the second moving mechanism is capable of moving at least three central primary transfer members, which are primary transfer members of at least three primary transfer sections arranged between the uppermost primary transfer member and the lowermost primary transfer member, between a contact position in contact with the latent image carrier via the intermediate transfer body and a separated position separated from the latent image carrier.

3. The transfer apparatus according to claim 2, wherein the first moving mechanism moves the downstream primary transfer member between the contact position and the separated position.

4. The transfer apparatus according to claim 3, wherein the first moving mechanism moves the first tension roller from the second position to the third position, and then the second moving mechanism moves each of the central primary transfer members from the separated position to the contact position.

5. The transfer apparatus according to claim 4, wherein the first moving mechanism moves the first tension roller from the second position to the third position, and the second moving mechanism moves each of the central primary transfer members from the separated position to the contact position, and the third moving mechanism moves the uppermost primary transfer member from the separated position to the contact position.

6. The transfer apparatus according to claim 4, wherein the first moving mechanism moves the first tension roller from the second position to the third position, and the uppermost primary transfer member maintains the contact position before and after the second moving mechanism moves each of the central primary transfer members from the separated position to the contact position.

7. The transfer apparatus according to claim 3, wherein the second moving mechanism moves each of the central primary transfer members from the contact position to the separated position, and then the first moving mechanism moves the first tension roller from the third position to the second position.

8. The transfer apparatus according to claim 3, wherein the first moving mechanism moves the first tension roller from a first position to a second position and moves the downstream primary transfer member from the contact position to the separated position, and then the third moving mechanism moves the upstream primary transfer member from the separated position to the contact position.

9. The transfer apparatus according to claim 3, wherein the third moving mechanism moves the uppermost primary transfer member from the contact position to the separated position, and then the first moving mechanism moves the first tension roller from the second position to the first position, and moves the lowermost primary transfer member from the separated position to the contact position.

10. The transfer apparatus according to claim 3, wherein the first moving mechanism moves the downstream primary transfer member and the first tension roller by a common drive source.

11. The first moving mechanism comprises a stepping motor, a photosensor for detecting the rotational position of the stepping motor, and a rotating body having a filler detected by the photosensor, The transfer apparatus according to claim 10, wherein the position of the first tension roller is changed based on the detection state of the photosensor.

12. A second tension roller for stretching the intermediate transfer body is further provided between the downstream primary transfer section and the primary transfer section one step upstream from the downstream primary transfer section. The transfer apparatus according to claim 2, wherein the downstream primary transfer member is separated from the intermediate transfer body, and the primary transfer member of the primary transfer section one level upstream from the downstream primary transfer section is in contact with the latent image carrier, and the second tension roller tensions the intermediate transfer body.

13. The transfer apparatus according to claim 12, wherein the second moving mechanism causes the second tension roller to come into contact with or separate from the intermediate transfer body.

14. The transfer apparatus according to claim 12, wherein the first moving mechanism causes the second tension roller to come into contact with or separate from the intermediate transfer body.

15. The transfer apparatus according to claim 1, wherein the downstream primary transfer section transfers a developer of a special color that is neither yellow, magenta, cyan, nor black to the intermediate transfer body.

16. Multiple latent image carriers, An image forming apparatus comprising a transfer apparatus according to any one of claims 1 to 15.

Images