Image forming apparatus

Abstract

To easily fit a cam side shaft coupling and a drive side shaft coupling to each other when mounting a detachable unit as compared with a case where an energization member for energizing a cam shaft when the cam shaft is not connected to a drive transmission shaft in a rotatable direction is provided on the detachable unit side in an image forming apparatus including the detachable unit.SOLUTION: An image forming apparatus includes: a movable body which is movably arranged in a support body of a detachable unit; a cam which moves the movable body; a cam shaft which is rotatably arranged in the support body and to which the cam is fixed; a cam side shaft coupling which is fixed to one end of the cam shaft and has a fitting section; a drive transmission shaft which is rotatably arranged in a main body side and to which a passive gear is fixed; a drive side shaft coupling which is fixed to one end of the drive transmission shaft and has a section to be fitted to which the fitting section is fitted; a movement transmission mechanism which is arranged on the main body side, is engaged with the passive gear and moves within a fixed range to transmit power; and an energization member which is arranged on the main body side and energizes the drive transmission shaft in a rotatable direction when the fitting section and the section to be fitted are not fitted to each other.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Patent Document 1, Japanese Patent No. 5181756, describes a driving force transmission device that includes a rotating member, a prevention member that prevents sliding between the side of the rotating member and other installed members, a transmission member that transmits the driving force from the rotating member to a driven body, and a biasing member that biases the transmission member in a direction away from the rotating member. Patent document 1 also describes that a portion of the biasing member in the driving force transmission device that is located on the rotating member side does not come into contact with the preventing member and is supported by the rotating member. Furthermore, Patent Document 1 also describes an image forming apparatus equipped with the drive force transmission device.

[0003] Japanese Patent Laid-Open Publication No. 11-85283, which is referred to as Patent Document 2, describes a position switching drive device that switches between at least two positions. Patent document 2 also describes that the position switching drive device has a drive means, a drive shaft driven by the drive means, a rotating member engaged with the drive shaft and rotating therewith, a return member arranged to be freely rotatable and engaging with the rotating member, and a biasing spring that biases the return member.

[0004] Patent Document 3, Japanese Patent No. 3861981, describes an image forming apparatus equipped with a separation mechanism and a separation mechanism drive means that applies a braking force when the separation mechanism comes into contact to reduce the impact of the contact, and applies a force to promote separation when the mechanism is separated, thereby achieving instantaneous separation. Patent document 3 also describes that the engagement / disengagement mechanism drive means comprises a rotation mechanism having a gear with a missing tooth portion that does not engage with the input gear and a rotor formed integrally with the gear with a stopper that stops every half rotation, and a spring member that engages with the gear at an eccentric position so as to apply a rotational force in a fixed direction to the rotation mechanism at the stopped position. Furthermore, Patent Document 3 also describes that the spring member applies a braking force when the separation mechanism contacts, and applies a force to promote separation when the mechanism separates. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5181756 (Claims 1 and 11) [Patent Document 2] JP-A-11-85283 (Claim 1) [Patent Document 3] Patent No. 3861981 (Claim 1) Summary of the Invention [Problem to be solved by the invention]

[0006] The problem that the present invention aims to solve is, in an image forming device that includes a detachable unit that is attached to a main body having an image forming section, a camshaft on which a cam that moves the moving body of the detachable unit is attached, a cam side shaft coupling fixed to one end of the camshaft, a drive transmission shaft that transmits power to the camshaft, and a drive side shaft coupling fixed to one end of the drive transmission shaft and engaging with the cam side shaft coupling, to make it easier to engage the cam side shaft coupling with the drive side shaft coupling when the detachable unit is attached. To explain further, an object of the present invention is to make it easier to engage the cam side shaft coupling and the drive side shaft coupling when the detachable unit is attached, compared to a case in which a biasing member is provided on the detachable unit side for biasing the cam shaft in a rotatable direction when it is not connected to the drive transmission shaft in the above-mentioned image forming apparatus. [Means for solving the problem]

[0007] The first aspect of the present invention is A main body having an image forming unit; A detachable unit having a support body that is detachably attached to the main body; A movable body that is movably disposed relative to the support and is biased in one direction; a cam that moves the moving body in a direction opposite to the one direction; a cam shaft rotatably disposed on the support and having the cam fixed thereto; a cam-side shaft coupling attached to one end of the camshaft and having a fitting portion; a drive transmission shaft rotatably disposed on the main body side and having a passive gear fixed thereto for receiving the power transmission; a drive-side shaft coupling attached to one end of the drive transmission shaft and having a fitted portion into which the fitting portion is fitted; a moving transmission body that is disposed on the main body side and meshes with the passive gear to move within a certain range to transmit power; a biasing member that is disposed on the main body side and biases the drive transmission shaft in a rotatable direction when the fitting portion and the fitted portion are not fitted to each other; The image forming apparatus includes:

[0008] A second aspect of the present invention is an image forming apparatus according to the first aspect, wherein the biasing member biases the drive side shaft coupling so that the range of motion of the drive side shaft coupling is wider than the range of motion of the cam side shaft coupling when the engaging portion and the engaged portion are not engaged.

[0009] A third aspect of the present invention is an image forming apparatus according to the second aspect of the invention, wherein the urging member is a tension spring having one end attached to a part of the main body and the other end attached to an eccentric portion of the other end of the drive transmission shaft.

[0010] A fourth aspect of the present invention is an image forming apparatus according to the first aspect of the present invention, wherein the removable unit is an intermediate transfer unit having an intermediate transfer belt that is rotated by being wound around a plurality of rotating rolls that are arranged on the support, and a plurality of primary transfer rolls that are arranged on the support and are urged by a primary urging member to come into contact with the intermediate transfer belt at portions that become a plurality of primary transfer positions on the inner circumferential surface of the intermediate transfer belt, The intermediate transfer unit is an image forming apparatus in which some of the plurality of primary transfer rolls are held in a state spaced apart from the intermediate transfer belt when the movable body is moved by the cam.

[0011] A fifth aspect of the present invention is an image forming apparatus according to the fourth aspect of the present invention, wherein the intermediate transfer unit includes a second cam that is fixed to a second cam shaft disposed on the support and that holds the remaining primary transfer rolls other than the part of the primary transfer rolls in a state of being moved to the inside of the intermediate transfer belt, and a lever that is fixed to the second cam shaft and is operated to move the second cam, The lever is an image forming apparatus that is operated to keep the remaining primary transfer roll in a state in which it has been moved to the inside of the intermediate transfer belt by the second cam when the intermediate transfer unit is being installed or removed. Effect of the Invention

[0012] According to the image forming apparatus of the first means described above, it is easier to engage the cam side shaft coupling and the drive side shaft coupling when the detachable unit is attached, compared to a case in which a biasing member that biases the cam shaft in a rotatable direction when it is not connected to the drive transmission shaft is provided on the detachable unit side.

[0013] According to the second means, the cam side shaft coupling and the drive side shaft coupling are easier to engage with each other even if the cam of the detachable unit moves the movable body and becomes immobile, compared to when the biasing member is configured to bias the cam side shaft coupling so that the range of motion of the cam side shaft coupling is wider than the range of motion of the drive side shaft coupling.

[0014] According to the third means, the biasing member can be easily made to function even if the drive transmission shaft rotates in the forward and reverse directions, compared to when the biasing member is a biasing member other than a tension spring.

[0015] According to the fourth means described above, it is possible to make it easier to engage the cam side shaft coupling and the drive side shaft coupling when installing the intermediate transfer unit, compared to a case in which a biasing member that biases the cam shaft in a rotatable direction when it is not connected to the drive transmission shaft is provided on the intermediate transfer unit side.

[0016] According to the fifth means, compared to the case where a biasing member that biases the cam shaft in a rotatable direction when it is not connected to the drive transmission shaft is provided on the removable unit side, it is possible to eliminate the need to operate a lever to release the immobilized state caused by the cam of the intermediate transfer unit moving the movable body. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing the inside of an image forming apparatus according to a first embodiment of the present invention as viewed from the front. [Diagram 2] 2 is a schematic diagram showing a state in which a portion of the image forming apparatus in FIG. 1, such as an intermediate transfer unit, which is a detachable unit, is viewed from above. FIG. [Diagram 3] 2 is a schematic diagram showing a state in which an intermediate transfer belt, a support frame, and other parts of an intermediate transfer unit are removed as viewed from above. FIG. [Figure 4] 2 is a schematic diagram of the inside of a main body of an image forming apparatus with an intermediate transfer unit removed, and the intermediate transfer unit removed. FIG. [Diagram 5] FIG. 1A is a schematic diagram of the inside of the intermediate transfer unit in a color mode, and FIG. 1B is a schematic diagram showing the intermediate transfer unit in FIG. [Figure 6] 1A is a schematic diagram of the inside of the intermediate transfer unit in the black-and-white mode, and FIG. 1B is a schematic diagram of the inside of the intermediate transfer unit when the intermediate transfer unit is being attached or detached. [Figure 7]FIG. 2 is a perspective view of a handle operating mechanism of the intermediate transfer unit and its surrounding area. [Figure 8] FIG. 2A is a schematic diagram showing a state of a mode switching device in a color mode, and FIG. 2B is a schematic diagram showing a state of the mode switching device in a black and white mode. [Figure 9] 1A is a perspective view showing the mode switching device in a color mode from an obliquely upper front side, and FIG. 1B is a perspective view showing the state of FIG. [Figure 10] FIG. 2 is a schematic plan view showing a part of a mode switching device. [Figure 11] FIG. 1A is a schematic diagram showing the state of a part of the mode switching device when the intermediate transfer unit is removed in color mode, as viewed from the front side, and FIG. 1B is a schematic diagram showing the state of FIG. 1A, as viewed from the rear side. [Figure 12] FIG. 1A is a schematic diagram showing the state of a part of the mode switching device when the intermediate transfer unit is removed in black and white mode, as viewed from the front side, and FIG. 1B is a schematic diagram showing the state of FIG. 1A, as viewed from the rear side. [Figure 13] 5 is an explanatory diagram illustrating the relationship between the ranges of motion of a drive-side shaft joint and a cam-side shaft joint of the mode switching device in the first embodiment. FIG. [Figure 14] (A) is a schematic diagram showing the main parts of a comparative intermediate transfer unit in color mode as viewed from the rear, and (B) is an enlarged schematic diagram showing the state when the first cam of the intermediate transfer unit in (A) has rotated to its maximum movable position. [Figure 15] (A) is a schematic diagram showing the main parts of a comparative intermediate transfer unit in black and white mode as viewed from the rear, and (B) is an enlarged schematic diagram showing the state when the lever operation corresponding to removing the intermediate transfer unit of (A) has been performed. [Figure 16] 11 is an explanatory diagram illustrating the relationship between the ranges of motion of a drive-side shaft joint and a cam-side shaft joint when a comparative intermediate transfer unit is used; FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described.

[0019] Embodiment 1 FIG. 1 is a schematic diagram of an image forming apparatus 1 according to the first embodiment of the present invention. In this specification and the drawings, the same reference numerals are used to denote substantially the same components, and redundant explanations of the same components will be omitted unless necessary.

[0020] (1) Overview of the image forming device The image forming apparatus 1 is an apparatus for forming a desired image on a sheet of paper. The image forming apparatus 1 according to the first embodiment is configured as an apparatus capable of forming an image corresponding to image information input from an external device. In this case, the external device is, for example, a personal computer, an information terminal, an image reading device, etc. Also, the image information is, for example, information about an image such as a character, a figure, a photograph, a pattern, etc.

[0021] 1, the image forming apparatus 1 includes a housing 10 which is an example of the main body of the image forming apparatus 1, an image forming unit 2, a paper supply device 4, an image processing unit (not shown), a power supply device, a control device, etc. The dashed dotted lines in Fig. 1 indicate the main transport paths along which paper 9 is transported inside the housing 10, etc.

[0022] The housing 10 is a box-shaped structure manufactured into a required external shape using materials such as structural materials for a framework, and exterior materials such as panels and opening / closing doors. The housing 10 in the first embodiment is configured as a housing having an external shape that is substantially a rectangular parallelepiped. As shown in Figures 1 and 2, when the surface facing a user of image forming apparatus 1 is defined as the front, housing 10 has a front surface (or front face) 10a, a back surface 10b, and left and right side surfaces 10c and 10d. Furthermore, the housing 10 is provided on its upper surface with a discharged paper receiving section 13 having a slope.

[0023] The image forming section 2 is a section for forming an image on a sheet 9 . The image forming section 2 in the first embodiment employs an electrophotographic image forming method and is composed of an imaging unit 20, an intermediate transfer unit 30 which is an example of a removable unit 15, and a fixing unit 38.

[0024] The imaging unit 20 is a unit that creates an image (toner image) made of a dry developer. The imaging unit 20 in the first embodiment employs four imaging units 20Y, 20M, 20C, and 20K that are dedicated to independently form toner images made of four colors, for example, yellow (Y), magenta (M), cyan (C), and black (K). The imaging units 20Y, 20M, 20C, and 20K are disposed inside the housing 10 so as to be lined up in series from the right side to the left side at regular intervals.

[0025] The imaging units 20Y, 20M, 20C, and 20K have almost the same configuration, except that they use different colors of developer. The imaging units 20Y, 20M, 20C, and 20K are configured as units equipped with a photosensitive drum 21, a charging device 22, an image exposure device 23, a developing device 24 (Y, M, C, K), a primary transfer roll 25, a drum cleaning device 26, etc., as shown in Figure 2 as a representative example of imaging unit 20K.

[0026] 1, only the reference numerals of the photosensitive drum 21 and the developing device 24 (Y, M, C) are shown for the imaging units 20 (Y, M, C) other than the imaging unit 20K, and the other reference numerals are omitted. The primary transfer roll 25 is generally an example of a primary transfer device, but is treated here as a part constituting the intermediate transfer unit 30 as described later.

[0027] In the imaging units 20Y, 20M, 20C, and 20K, when an image forming operation is started, a toner image made of the above four colors is formed as necessary. Taking the imaging unit 20K as a representative example, first the photosensitive drum 21 starts to rotate in the direction of the arrow shown in Fig. 1. Then, the outer peripheral surface (image forming surface) of the photosensitive drum 21 is charged by the charging device 22 to a uniform surface potential. Then, the charged image forming surface of the photosensitive drum 21 is exposed to light based on image information by the image exposure device 23, and an electrostatic latent image is formed. Thereafter, the electrostatic latent image is developed on the outer peripheral surface of the photosensitive drum 21 with black toner supplied from the developing device 24K, and a black toner image is formed. In the remaining imaging units 20Y, 20M, and 20C, yellow, magenta, and cyan toner images are formed on the outer circumferential surfaces of the respective photosensitive drums 21, respectively.

[0028] The intermediate transfer unit 30 is a unit that temporarily holds the image created by the image creating unit 20 and then transfers it onto the paper 9 . 1 etc., the intermediate transfer unit 30 in the first embodiment is configured as a unit including an intermediate transfer belt 31, belt holding rolls 32, 33, 34, 35, primary transfer rolls 25Y, 25M, 25C, 25K, a secondary transfer device 36, a belt cleaning device 37, etc. The belt holding rolls 32, 33, 34, 35 are an example of a plurality of rotating rolls around which the intermediate transfer belt 31 is wound. Furthermore, the intermediate transfer unit 30 is disposed inside the housing 10 above the image forming units 20Y, 20M, 20C, and 20K.

[0029] In the intermediate transfer unit 30, the positions at which the photosensitive drums 21 of the imaging units 20Y, 20M, 20C, and 20K come into contact with the outer circumferential surface of the intermediate transfer belt 31 correspond to primary transfer positions. In the intermediate transfer unit 30, the position where the secondary transfer roll, which is a contact transfer member of the secondary transfer device 36, contacts the outer circumferential surface of the intermediate transfer belt 31 becomes the secondary transfer position.

[0030] In the intermediate transfer unit 30, when an image forming operation begins, the intermediate transfer belt 31 receives the power of the belt support roll 32 and starts to rotate in the direction indicated by the arrow in FIG. Next, in the intermediate transfer unit 30, the toner images formed by all or some of the imaging units 20Y, 20M, 20C, and 20K are primarily transferred to the outer circumferential surface of the intermediate transfer belt 31 at the primary transfer position. At this time, the toner images are primarily transferred by the transfer action of the primary transfer roll 25. Next, in the intermediate transfer unit 30, the toner image that has been primarily transferred onto the outer peripheral surface of the intermediate transfer belt 31 is secondarily transferred onto the paper 9 at the secondary transfer position. At this time, the toner image is secondarily transferred by the transfer action of the secondary transfer device 36. The paper 9 is supplied from the paper supply device 4 or the like, as described later. The intermediate transfer unit 30 will be described in further detail below.

[0031] The fixing unit 38 is a unit that fixes the unfixed toner image transferred onto the paper 9 onto the paper 9 . As shown in FIG. 1, the fixing unit 38 in the first embodiment is configured as a unit including a unit housing 38a, a heating rotation member 38b, a pressurizing rotation member 38c, and the like. The heating rotating member 38b and the pressurizing rotating member 38c are rotating bodies in the form of a roll, a belt, or the like (including a combination thereof).

[0032] In addition, the fixing unit 38 has a contact portion, where the heating rotation member 38b and the pressurizing rotation member 38c come into contact with each other substantially along the direction of the rotation axis, as a fixing processing portion. Furthermore, the fixing unit 38 is disposed inside the housing 10 at a position above the secondary transfer position of the intermediate transfer unit 30 .

[0033] In the fixing unit 38, when the image forming operation starts, the heating rotating member 38b and the pressurizing rotating member 38c start to rotate, and the heating rotating member 38b is heated to the fixing temperature. Next, in the fixing unit 38, the paper 9 onto which the toner image has been secondarily transferred by the intermediate transfer unit 30 is introduced into the contact portion and passed through. As a result, the fixing unit 38 heats and melts the unfixed toner image under pressure, thereby fixing it to the paper 9.

[0034] The paper supply device 4 is a device that stores paper 9 on which an image is to be formed and supplies it to the image forming section 2. The paper feeder 4 in the first embodiment includes a storage tray 41, a sending device 42, and the like. The storage tray 41 is a structure that stacks and stores paper sheets 9 of a predetermined size. The storage tray 41 is provided, for example, in a state that it can be pulled out to the front (front face) 10a side of the housing 10. The sending device 42 is a device that sends out the paper sheets 9 stored in the storage tray 41 one by one, starting from the top one. Two or more sets of the storage tray 41 and the delivery device 42 may be provided. The paper 9 is a recording medium on which an image made of a developer can be formed. The paper 9 also includes media other than pulp paper, such as coated paper and resin sheets.

[0035] In the image forming apparatus 1, a supply conveying path, a discharge conveying path, a relay conveying path, and the like are provided inside a housing 10, as illustrated by dashed lines in FIG.

[0036] The supply transport path is a transport path that supplies the paper 9 sent out from the paper supply device 4 to the image forming unit 2. The supply transport path is made up of a plurality of transport roll pairs 44, 45 and a paper guide member (not shown). The discharge conveying path is a conveying path that conveys the paper 9 on which an image has been formed in the image forming unit 2 so as to be discharged through the discharge outlet 14 to the discharged paper storage unit 13. The discharge conveying path is composed of a plurality of conveying roll pairs 46, 47 and a paper guide member (not shown). The relay transport path is a transport path that transports the paper 9 that has passed through the secondary transfer position of the image forming section 2 to the fixing unit . The relay transport path is formed by a paper guide member , for example.

[0037] In the paper supply device 4, when an image forming operation is started, a sheet of paper 9 is sent out from a storage tray 41 by a sending device 42 toward a supply conveying path. Next, the paper 9 sent to the supply transport path is transported by the transport roll pair 45 in accordance with the secondary transfer timing to the secondary transfer position of the intermediate transfer unit 30. At this time, the toner image is secondarily transferred onto the paper 9 by passing through the secondary transfer position. Subsequently, the paper 9 onto which the toner image has been secondarily transferred is introduced into the fixing unit 38 in the image forming section 2, where a fixing process is performed, and then the paper 9 is sent to a discharge conveyance path.

[0038] Finally, the paper 9 on which the image has been fixed is transported to the discharge outlet 14 through a discharge transport path, and then discharged to and stored in the discharged paper storage section 13. With the above, the image forming operation on one side of the paper 9 by the image forming apparatus 1 is completed.

[0039] The image forming apparatus 1 is configured to perform image forming operations by switching between a color mode for forming a color (multi-color) image and a black-and-white mode for forming a black-and-white image, which is an example of a monochromatic image.

[0040] The color mode is an operating mode in which all four imaging units 20Y, 20M, 20C, and 20K are operated to form a so-called full-color image by superimposing four-color (Y, M, C, K) toner images formed by each imaging unit 20 (Y, M, C, K). The black and white mode is an operation mode in which only the imaging unit 20K is operated to form a black and white image constituted by a black toner image formed by the imaging unit 20K. The color mode and the black and white mode can be arbitrarily selected by the user using a setting image when issuing a command for an image forming operation, for example. The mode setting information is determined by a control device (not shown).

[0041] As shown in FIG. 4, the image forming apparatus 1 is configured such that the intermediate transfer unit 30, except for the secondary transfer device , is detachably attached to the housing .

[0042] As shown in FIG. 2, the intermediate transfer unit 30 is attached and detached by inserting and removing it in the directions indicated by arrows E1 and E2 on the front side, which is the front surface 10a of the housing 10. 4, the housing 10 is provided with a mounting section 16 that has an opening at the front side and into which the intermediate transfer unit 30 can be mounted. The mounting section 16 is formed as a portion that is exposed to the outside when an exterior door (not shown) on the front surface 10a of the housing 10 or an interior door (not shown) inside the housing 10 is opened.

[0043] The mounting section 16 shown in Fig. 4 is configured so that the four imaging units 20Y, 20M, 20C, and 20K can also be detachably mounted. Correspondingly, the imaging units 20Y, 20M, 20C, and 20K are configured so that the entirety of the imaging units 20Y, 20M, 20C, and 20K can be detachably mounted, or so that only the remaining parts of the imaging units 20Y, 20M, 20C, and 20K can be detachably mounted. Examples of the parts of the units include the image exposure device 23 and the developing device 24.

[0044] Furthermore, as shown in FIG. 2, the image forming apparatus 1 has a drive unit 6 disposed inside the rear side of the housing 10, which generates and transmits rotational power to the rotating components in the image forming unit 2.

[0045] The drive unit 6 has a main body 61 in which a motor, a reduction gear mechanism, etc. are arranged inside a housing, and a drive transmission unit 62 that transmits power from the main body 61 to a predetermined transmission destination. The drive transmission unit 62 has a gear train (not shown) that receives power from the main body 61 and distributes it, adjusts the speed, etc., and a drive transmission shaft (not shown) that transmits power to the transmission destination arranged in the housing.

[0046] The drive transmission section 62 includes a plurality of drive transmission shafts that transmit power to each photosensitive drum 21 and developing device 24 (Y, M, C, K) in the image-forming units 20Y, 20M, 20C, 20K, a drive transmission shaft that transmits power to the belt support roll 32 in the intermediate transfer unit 30, and the like. In addition, as shown in FIG. 2, the drive transmission shaft that transmits power to the belt support roll 32 is provided with a drive side shaft coupling 63 that is fitted and connected to a passive side shaft coupling 39 of the belt support roll 32, which will be described later, when the intermediate transfer unit 30 is installed.

[0047] (2-1) Configuration for switching modes of intermediate transfer unit The configuration regarding mode switching of the intermediate transfer unit 30 will be described in detail below. The intermediate transfer unit 30 is configured so that the state (shape) of the intermediate transfer belt 31 is changed in response to switching between the above-mentioned color mode and black-and-white mode.

[0048] In other words, when switched to the color mode, as shown in Figures 1 and 5, the intermediate transfer belt 31 is brought into contact with each of the photosensitive drums 21 in the four imaging units 20Y, 20M, 20C, and 20K involved in the image forming operation in the color mode. The state of the intermediate transfer belt 31 at this time is realized by the primary transfer rolls 25Y, 25M, 25C, and 25K moving to and existing at their respective transfer (operation) positions.

[0049] Also, when switched to the black-and-white mode, as shown in FIG. 6(A), the intermediate transfer belt 31 is brought into contact only with the photosensitive drum 21 in the black imaging unit 20K involved in the image forming operation in the black-and-white mode. As a result, the intermediate transfer belt 31 is separated from the photosensitive drums 21 of the three imaging units 20Y, 20M, and 20C that are not involved in the image forming operation in the black-and-white mode, that is, is in a non-contact state. The state of the intermediate transfer belt 31 at this time is realized by the primary transfer rolls 25Y, 25M, and 25C being moved to and present at their respective retreat positions.

[0050] First, as shown in FIG. 2 and FIG. 3, the intermediate transfer unit 30 includes front and rear support frames 50F and 50R, which are an example of a support body. The support frames 50F and 50R are frames that support parts such as the belt support rolls 32 and 33 as described below, and also frames that maintain the framework of the intermediate transfer unit 30.

[0051] The support frames 50F, 50R in the first embodiment are configured as plate-like frames having a length sufficient to support the belt support rolls 32, 33 with a predetermined distance between them. The support frames 50F, 50R are disposed in parallel at positions in front of and behind the intermediate transfer unit 30 with a predetermined gap therebetween. Furthermore, the support frames 50F, 50R are connected by, for example, two connecting frames 50J, thereby forming an integrated unit.

[0052] As shown in Figs. 3 and 5, belt support rolls 32, 33 are rotatably supported by bearings 321, 331, respectively, on both ends of the support frames 50F, 50R in the longitudinal direction (left-right direction in the drawings).

[0053] The belt support roll 32 is configured as a drive roll that provides power to rotate the intermediate transfer belt 31 in a predetermined direction indicated by an arrow (see FIG. 1). For this reason, the belt holding roll 32, which is a drive roll, has a passive side shaft coupling 39 fixedly attached to one end of its rotating shaft (not shown) as shown in Figures 2 and 3. The passive side shaft coupling 39 is attached to the end of the rotating shaft of the belt holding roll 32 that protrudes outward beyond the rear support frame 50R. Here, the shaft joint is also called a coupling (hereinafter the same).

[0054] The belt support roll 33 is configured as a tension applying roll that applies a predetermined tension to the intermediate transfer belt 31 . Therefore, a predetermined pressure is applied to the bearing 331 of the belt support roll 33 by a pressure applying mechanism 332 in a direction away from the belt support roll 32 as shown in FIG. The pressure applying mechanisms 332 are attached to the support frames 50F, 50R, respectively. The pressure applying mechanisms 332 are each configured to include a compression coil spring (not shown) that generates a spring force and has one end fixed to the support frames 50F, 50R, respectively.

[0055] As shown in FIG. 3, the belt support rolls 34, 35 are indirectly supported by the support frames 50F, 50R, respectively. Both of the belt support rolls 34 and 35 are configured as surface-finishing rolls that support a part 31j of the intermediate transfer belt 31 so as to form the part 31j as a primary transfer surface.

[0056] 5, the belt support roll 34 is supported by support frames 50F and 50R so as to swing about a support shaft 501. The swinging frames are also called swinging links (hereinafter the same). 5, the belt support roll 35 is rotatably supported by a bearing 351 that swings relative to the support frames 50F, 50R. The bearing 351 is connected to the bearing 321 of the belt support roll 32 and is provided at the end of a connection frame 355 that swings about the bearing 321 as a fulcrum.

[0057] The oscillating frame 57H has two arms that protrude in two different directions and form a predetermined angle with the support shaft 501 as the center. The swing frame 57H rotatably supports both ends of the shaft of the belt support roll 34 on one arm portion thereof via bearings (not shown). Further, a tension coil spring 59h, which is an example of a pressure biasing member, is disposed on the other arm of the oscillating frame 57H.

[0058] One end of the tension coil spring 59h is attached to a portion of the support frame 50F, 50R on the opposite side of the support shaft 501 from the belt holding roll 34 and closer to the belt holding roll 33. The other end of the tension coil spring 59h is attached so as to be hooked onto a part of one of the arms of the swing frame 57H. As a result, the tension coil spring 59h biases the swing frame 57H to swing in a direction in which the belt support roll 34 approaches the inner circumferential surface of the intermediate transfer belt 31. The biasing force at this time is a force that pulls in the direction shown by the solid arrow drawn adjacent to the tension coil spring 59h in Fig. 5(A) and is slightly diagonally downward and to the right in Fig. 5(A).

[0059] The swing frame 57H swings about a support shaft 501 between an operating position and a retracted position. The operating position of the swing frame 57H is a position where the belt support roll 34 is moved so that the intermediate transfer belt 31 is displaced outward, and a portion 31j of the intermediate transfer belt 31 is maintained in a state where it forms the primary transfer surface. The retracted position of the oscillating frame 57H is the position when the belt support roll 34 is moved so that the intermediate transfer belt 31 is displaced inward, and a portion 31j of the intermediate transfer belt 31 is kept retracted inward from the position that forms the primary transfer surface. The movement of the oscillating frame 57H to the retracted position is performed when the monochrome mode is switched to. The movement of the oscillating frame 57H to the retracted position also results in the movement of the belt support roll 35 to the retracted position.

[0060] A bearing 351 supporting the belt support roll 35 swings about a bearing 321 between an operating position and a retracted position. The operating position of the bearing 351 is a position where the belt support roll 35 is moved so that the intermediate transfer belt 31 is displaced outward, and a part 31j of the intermediate transfer belt 31 is maintained in a state where it forms the primary transfer surface. The retracted position of the bearing 351 is the position when the belt support roll 35 is moved so that the intermediate transfer belt 31 is displaced inward, and a part 31j of the intermediate transfer belt 31 is kept retracted inward from the position that forms the primary transfer surface.

[0061] The bearing 351 is switched between an operating position and a retracted position by the action of a second cam 520, which will be described later, and is held at each of the positions. The movement of the bearing 351 to the retracted position is performed when performing the installation or removal of the intermediate transfer unit 30. In addition, the movement of the bearing 351 to the retracted position ultimately results in the movement of the belt support roller 35 to the retracted position.

[0062] Further, the primary transfer rolls 25Y, 25M, 25C, and 25K are indirectly supported by the support frames 50F and 50R via swing frames 57Y, 57M, 57C, and 57K, respectively.

[0063] The oscillating frames 57Y, 57M, 57C, and 57K each have a shape having two arms that sandwich a support shaft 501 and protrude in two different directions forming a predetermined angle therebetween. The swing frames 57Y, 57M, 57C, and 57K each rotatably support both ends of the shaft of the primary transfer rolls 25Y, 25M, 25C, and 25K on one arm portion thereof via a bearing (not shown). Further, compression coil springs 59y, 59m, 59c, and 59k, which are an example of a pressure biasing member, are disposed on the other arm portions of the oscillating frames 57Y, 57M, 57C, and 57K, respectively.

[0064] The compression coil springs 59y, 59m, 59c, and 59k have one end fixed to a spring attachment portion (not shown) of the support frames 50F and 50R, respectively, and the other end of each of the compression coil springs 59y, 59m, 59c, and 59k is disposed so as to contact a part of one arm portion of the oscillating frames 57Y, 57M, 57C, and 57K. As a result, the compression coil springs 59y, 59m, 59c, and 59k each bias the oscillating frames 57Y, 57M, 57C, and 57K so that the primary transfer rolls 25Y, 25M, 25C, and 25K each oscillate in a direction that brings the intermediate transfer belt 31 closer to each primary transfer position.

[0065] The biasing force at this time also serves as a pressure applied when the primary transfer rolls 25Y, 25M, 25C, and 25K bring the intermediate transfer belt 31 into contact with each of the photosensitive drums 21 of the imaging units 20Y, 20M, 20C, and 20K at the primary transfer position. The biasing force at this time acts in the direction indicated by the solid arrows drawn adjacent to the compression coil springs 59y, 59m, 59c, and 59k in Fig. 5(A). The biasing force of the compression coil springs 59y, 59m, and 59c all points obliquely to the upper right in Fig. 5(A). The biasing force of the compression coil spring 59k points slightly obliquely to the lower left in Fig. 5(A).

[0066] The oscillating frames 57Y, 57M, 57C, and 57K oscillate about the respective support shafts 501 between an operating position and a retracted position. The operating positions of the oscillating frames 57Y, 57M, 57C, and 57K are positions, as shown in FIG. 5 etc., when the primary transfer rolls 25Y, 25M, 25C, and 25K are moved so that a portion 31j of the intermediate transfer belt 31 is kept in contact with each of the photosensitive drums 21 of the imaging units 20Y, 20M, 20C, and 20K, respectively. In addition, the retracted positions of the oscillating frames 57Y, 57M, 57C, and 57K are positions when the primary transfer rolls 25Y, 25M, 25C, and 25K are moved so that a portion 31j of the intermediate transfer belt 31 is kept retracted away from each photosensitive drum 21 of the imaging units 20Y, 20M, 20C, and 20K, as shown in FIG. 6.

[0067] The movement of the oscillating frames 57Y, 57M, and 57C to their retracted positions is performed when the monochrome mode is switched to. The movement of the oscillating frames 57Y, 57M, and 57C to their retracted positions ultimately results in the movement of the primary transfer rolls 25Y, 25M, and 25C to their retracted positions. The movement of the oscillating frame 57K to the evacuation position is performed when performing the installation or removal of the intermediate transfer unit 30. This movement of the oscillating frame 57K to the evacuation position ultimately results in the movement of the primary transfer roll 25K to the evacuation position.

[0068] Next, as shown in FIGS. 2, 3, 5, etc., the intermediate transfer unit 30 includes front and rear moving frames 51F and 51R, which are an example of a moving body. In FIG. 5, some components such as the support frames 50F and 50R and the connecting frame 50J are not shown.

[0069] The movable frames 51F and 51R are frames that move when switching between the color mode and the black and white mode, and have the function of swinging the swingable frames 57Y, 57M, 57C, and 57H to their respective operating positions or retracted positions. Therefore, the moving frames 51F and 51R also function as a part of the mode switching device 7, which will be described later.

[0070] The moving frames 51F and 51R are configured as plate-like frames that are positioned at least between the belt support rolls 32 and 33 and have a length that enables them to move a predetermined distance. As shown in FIG. 3 and other figures, the moving frames 51F and 51R are disposed on the inner sides of the support frames 50F and 50R. Furthermore, as shown in FIGS. 3, 5, etc., the moving frames 51F, 51R are supported so as to be movable in the directions indicated by arrows D1, D2 relative to the supporting frames 50F, 50R.

[0071] The moving frames 51F, 51R in the first embodiment are movably supported by a support shaft 56 disposed between the support frames 50F, 50R and a first cam shaft 53, which will be described later.

[0072] More specifically, as shown in Fig. 5, the moving frames 51F, 51R are provided with movement guide elongated holes 512, 516 in a portion thereof. The movement guide elongated holes 512, 516 are formed as through holes having an elongated shape along the directions (D1, D2) in which the moving frames 51F, 51R should move. The movement guide elongated holes 516 are provided in the side surface of a cam accommodating portion 514, which will be described later. The moving frames 51F, 51R are in a state in which the support shaft 56 penetrates the moving guide long hole 512, and the first cam shaft 53 penetrates the moving guide long hole 516. In this way, the moving frames 51F, 51R are supported so as to slide and move on the support shaft 56 and the first cam shaft 53. In the first embodiment, a cylindrical mounting portion fixed to a first cam shaft 53 of the first cams 52F, 52R (described later) penetrates the movement guide long hole 516. As a result, the moving frames 51F, 51R are slidably supported on the first cam shaft 53 via the mounting portion of the first cams 52F, 52R.

[0073] When the mode is switched to the color mode, the moving frames 51F and 51R are in a state of having moved in the direction indicated by the arrow D1 as shown in FIG. At this time, the movement of the movable frames 51F, 51R in the direction indicated by the arrow D1 is achieved by releasing the action of the front first cam 52F and the rear first cam 52R and receiving the urging force in the direction of the arrow D1 from the following springs. The biasing force received at this time is of two types: one is a component force of the spring force of the tension coil spring 59h arranged in the oscillating frame 57H, which is in the direction indicated by the arrow D1, and the other is a component force of the spring force of the compression coil springs 59y, 59m, and 59c arranged in the oscillating frames 57Y, 57M, and 57C, which is in the direction indicated by the arrow D1.

[0074] Furthermore, when the mode is switched to black and white, the moving frames 51F and 51R are in a state of having moved in the direction indicated by the arrow D2 as shown in FIG. 6(A). At this time, the movement of the moving frames 51F, 51R in the moving direction D2 is performed by the action of the front first cam 52F and the rear first cam 52R.

[0075] As shown in FIG. 3 and FIG. 5, the first cams 52F, 52R are plate cams having an eccentric shape. The first cams 52F, 52R are disposed in a state of being housed in the respective cam housing portions 514 of the moving frames 51F, 51R.

[0076] The cam accommodating portion 514 is a portion that accommodates the first cams 52F, 52R in a state in which they can rotate within a predetermined range. The cam accommodating portion 514 is provided on the inside of a position between the swing frame 57K of the primary transfer roll 25K and the swing frame 57C of the primary transfer roll 25C of the moving frames 51F and 51R. The cam accommodating portion 514 is provided as a portion having a substantially three-dimensional recessed shape extending from the top to the bottom of the moving frames 51F, 51R. Furthermore, the cam accommodating portion 514 forms an inner wall surface of the primary transfer roll 25K closer to the swing frame 57K as a cam contact surface 515 with which the first cams 52F, 52R come into contact and act.

[0077] As shown in FIGS. 3 and 5, the first cams 52F, 52R are fixed to first cam shafts 53 that are rotatably supported by the support frames 50F, 50R, respectively. Furthermore, the first cams 52F, 52R are configured to have a shape having a cam action portion 52a that is eccentric by a predetermined dimension from the first cam shaft 53. The amount of eccentricity of the cam action portion 52a of the first cams 52F, 52R is a dimension required to move the moving frames 51F, 51R by a predetermined distance in the moving direction indicated by the arrow D2. The cam action portions 52a of the first cams 52F, 52R exert a cam action when they come into contact with the cam contact surfaces 515 of the cam accommodating portions 514, respectively.

[0078] As shown in FIG. 3 and FIG. 5, the first cam shaft 53 is disposed so that one end thereof protrudes outside (further rearward) from the rear moving frame 51R. Further, a cam side shaft coupling 54 is fixedly attached to one end of the first cam shaft 53.

[0079] 10, the cam-side shaft coupling 54 has a cylindrical main body 54a that is open at one end, and a fitting portion 55 is provided in a part of the main body 54a. The fitting portion 55 is a portion that fits with a fitted portion (74) of a drive-side shaft coupling (73) that will be described later.

[0080] Fitting portion 55 in the first embodiment is configured as a plate-like structural part provided in a part of the opening of cylindrical main body 54a. The plate-like structural part of fitting portion 55 is a plate-like protruding part that protrudes at a predetermined height from a part of the opening of main body 54a toward the center of the cylinder and extends linearly toward the rear side inside the opening. As shown in FIG. 10, the cam-side shaft coupling 54 is provided on the inner peripheral surface of its cylindrical main body 54a with gear teeth 54g for receiving the rotational power to be transmitted.

[0081] Furthermore, as shown in Figs. 3, 5, 6, etc., the moving frames 51F, 51R are provided with front and rear pushing portions 58h, 58y, 58m, 58c protruding from their inner sides.

[0082] The pushing portions 58h, 58y, 58m, and 58c are protruding portions that contact and push the other arm portions of the front and rear oscillating frames 57H, 57Y, 57M, and 57C, respectively, when the moving frames 51F, 51R move in the direction indicated by the arrow D2. Therefore, as shown in FIG. 6(A), when the moving frames 51F, 51R move in the direction indicated by the arrow D2, the pushing portions 58h, 58y, 58m, 58c move integrally in the same direction.

[0083] As a result, the pushing portion 58h comes into contact with a contact surface portion of the other arm portion of the oscillating frame 57H on the same side as the side to which one end of the tension coil spring 59h is attached, and the pushing portions 58y, 58m, and 58c come into contact with contact surfaces of the other arm portions of the oscillating frames 57Y, 57M, and 57C on the opposite side to the side to which the other ends of the compression coil springs 59y, 59m, and 59c come into contact.

[0084] The moving frames 51F, 51R are acted upon by the first cams 52F, 52R to move a predetermined distance in the direction indicated by the arrow D2. In conjunction with the movement of the moving frames 51F, 51R, the pushing portions 58h, 58y, 58m, 58c come into contact with the contact surfaces of the other arm portions of the oscillating frames 57H, 57Y, 57M, 57C, respectively, and push in the direction indicated by arrow D2.

[0085] As a result, the oscillating frames 57H, 57Y, 57M, and 57C each oscillate about the support shaft 501 as a fulcrum by the amount of pressure, as indicated by the dashed arrows in FIG. 6(A), and oscillate from each operating position to the retracted position. At this time, the oscillating frame 57H receives a spring force Fh by pulling the tension coil springs 59h as shown by solid arrows in Fig. 6(A), and the oscillating frames 57Y, 57M, and 57C receive spring forces F1y, F1m, and F1c by compressing the compression coil springs 59y, 59m, and 59c, respectively.

[0086] (2-2) Configuration related to installation and removal of intermediate transfer unit In addition, when the intermediate transfer unit 30 is attached or detached, the intermediate transfer belt 31 is moved away from the photosensitive drum 21 in the image creating unit 20K and retracted, as shown in FIG. 6(B). With this configuration, when the intermediate transfer unit 30 is attached or detached, the intermediate transfer belt 31 is separated from all of the photosensitive drums 21 of the four imaging units 20 (Y, M, C, K) as shown in Fig. 6(B). At this time, the intermediate transfer belt 31 that is actually separated is a portion 31t located on the side facing each of the photosensitive drums 21 of the imaging units 20 (Y, M, C, K).

[0087] The intermediate transfer unit 30 employs a lever operation mechanism that operates a lever 95 to change the state of the intermediate transfer belt 31 when performing attachment and detachment operations.

[0088] The lever operating mechanism is a mechanism that moves the primary transfer roll 25K and the bearings 351 of the belt support roll 35 to the inside of the intermediate transfer belt 31 by operating the lever 95 to tilt in a predetermined direction, as shown in Figure 6 (B). As shown in FIGS. 5 to 7, the lever operation mechanism includes a second cam shaft 561, a lever 95, front and rear second cams 520F, 520R, front and rear relay swing frames 57J, and the like.

[0089] The second cam shaft 561 is rotatably provided in a portion of the support frames 50F, 50R between the swing frame 57K and the belt support roll 32 (the bearing 321 thereof). Moreover, the second cam shaft 561 is attached in a state where one end thereof protrudes outward (toward the front side) of the front support frame 50F.

[0090] The lever 95 is attached so as to be fixed to one end of the second cam shaft 561 that protrudes outward from the front support frame 50F. As shown in Figures 3 and 7, the lever 95 has a cylindrical mounting portion 95a into which one end of the second cam shaft 561 is fitted and attached, and a lever portion 95b extending radially from the front end of the mounting portion 95a. 5 and 7, the lever 95 can be swung about the second cam shaft 561 in the directions indicated by the arrows M1 and M2.

[0091] The lever 95 swings between an attached position and a detached position. The mounting position of the lever 95 is a position where the intermediate transfer unit 30 is temporarily mounted in the mounting portion 16 and then the temporary mounting is moved to the proper mounting position and maintained there. This mounting position is set to a position where the lever 95 is tilted a predetermined amount in the direction indicated by the arrow M1, as shown in FIG. 5 etc. The attachment / detachment position of the lever 95 is a position for maintaining a safe attachment / detachment operation when removing the intermediate transfer unit 30 from the mounting part 16 and when temporarily mounting it in the mounting part 16. This attachment / detachment position is set to a position when the lever 95 is tilted a predetermined amount in the direction indicated by the arrow M2, as shown in FIG.

[0092] 7, the lever 95 is provided with a protrusion 95c on the outer circumferential surface of the mounting portion 95a thereof. Correspondingly, the front support frame 50F is provided with two rotation-stopping projections (not shown) with which the protrusion 95c can come into contact. As a result, when the protrusions 95c come into contact with the rotation-stopping projections during operation of the lever 95, the lever 95 stops swinging at its maximum swingable position. This maximum swingable range is set at a position slightly shifted outward from the mounting position and the mounting / detaching position of the lever 95 with a margin therebetween.

[0093] The front and rear second cams 520F, 520R are configured as plate cams having an eccentric shape as shown in Figures 5 to 7. In addition, both of the second cams 520F, 520R are configured as cams that act on the bearing 351 of the belt holding roll 35 and the intermediate swing frame 57J, respectively. Furthermore, the second cams 520F, 520R are attached so as to be fixed to a portion of the second cam shaft 561 between the front support frame 50F and the lever 95.

[0094] The front and rear intermediate swing frames 57J are frames that swing the front and rear swing frames 57K of the primary transfer roll 25K in predetermined directions by the action of the second cams 520F, 520R. The intermediate swing frame 57J swings about support shafts 502 provided at portions of the support frames 50F, 50R between the second cams 520F, 520R and the swing frame 57K.

[0095] Further, as shown in FIG. 5 and FIG. 6, the intermediate swing frame 57J is formed as a frame having a shape having a cam contact portion and a swinging portion that protrude in two different directions on either side of the support shaft 501. The cam contact portions are portions that come into contact with the second cams 520F, 520R and are acted upon by the cams. The swing action portion is a portion that comes into contact with the swing receiving portion 571 of the swing frame 57K and swings the swing frame 57K toward the retracted position.

[0096] In addition, as shown in Figure 7 etc., the second cams 520F, 520R are configured in a shape having a first cam action portion 521 and a second cam action portion 522 that contact the bearing 351 of the belt holding roll 35 and the cam contact portion of the intermediate oscillating frame 57J.

[0097] The first cam action portion 521 is an action surface portion that is eccentric by a dimension required to move the bearing 351 of the belt support roll 35 from its retracted position to its operating position. The first cam action portion 521 is provided with a pair of banks 523 to stop and stabilize the bearing 351 on the surface portion. Further, the second cam action portion 522 is an action surface portion that is eccentric by a dimension required to move the cam contact portion of the intermediate swing frame 57J from the retracted position to the operating position. Furthermore, the second cams 520F, 520R are provided with recessed surface portions that keep the bearings 351 of the belt support roll 35 in the retracted position when the second cam action portions 522 come into contact with the cam contact portions of the intermediate swing frame 57J.

[0098] When the intermediate transfer unit 30 is temporarily attached by inserting it into the attachment portion 16 of the housing 10, the lever operation mechanism performs an operation to swing the lever 95 in the direction indicated by the arrow M1 and to keep it in the attachment position.

[0099] When the lever 95 is operated to remain in the mounting position, as shown in FIG. 5 etc., the operation of the lever 95 causes the second cam shaft 561 and the second cams 520F, 520R to rotate in the direction indicated by the arrow M1. As a result, the first cam action portions 521 of the front and rear second cams 520F, 520R come into contact with the bearings 351 of the belt support roll 35, moving the bearings 351 to the operating positions. As a result, the belt support roll 35 supported by the bearing 351 moved to the operating position holds the part 31j of the intermediate transfer belt 31 in a state in which it forms a surface-finished surface for primary transfer, as shown in FIG. 5 and other figures.

[0100] At this time, as shown in FIG. 5 and other figures, the second cam action portions 522 of the second cams 520F, 520R are kept out of contact with the intermediate swing frame 57J. As a result, the intermediate oscillating frame 57J is not affected by the cam action of the second cam 520 and is in a free state, so that no action is exerted on the intermediate oscillating frame 57J. As a result, the oscillating frame 57K is oscillated by the biasing force of the compression coil spring 59K and moves to the operating position. As a result, in the intermediate transfer unit 30, as shown in Figure 5, the primary transfer roll 25K supported by the oscillating frame 57K moved to the operating position keeps the intermediate transfer belt 31 in contact with the photosensitive drum 21 of the image-forming unit 20K.

[0101] When the intermediate transfer unit 30 is attached to or detached from the attachment portion 16 of the housing 10, the lever operation mechanism swings the lever 95 in the direction indicated by the arrow M2 and holds it in the attachment / detachment position.

[0102] When the lever 95 is operated to remain in the attachment / detachment position, as shown in FIG. 6B and FIG. 7, the operation of the lever 95 causes the second cam shaft 561 and the second cams 520F, 520R to rotate in the direction indicated by the arrow M2. As a result, the first cam action portions 521 of the front and rear second cams 520F, 520R are separated from the bearing 351 of the belt holding roll 35, and the bearing 351 moves to the retracted position. At this time, the bearing 351 is kept in contact with the recessed surface portion of the second cam 520 and stopped at the retracted position. As a result, the belt support roll 35 supported by the bearing 351 moved to the retracted position holds the portion 31t of the intermediate transfer belt 31 in a state released from the state of forming the primary transfer surface, as shown in FIG. 6B.

[0103] Also at this time, as shown in Figure 6 (B), the second cam action portion 522 of the second cam 520F contacts the cam contact portion of the relay oscillating frame 57J, causing the oscillating action portion of the relay oscillating frame 57J to contact the oscillating receiving portion 571 of the oscillating frame 57K and push up. As a result, the oscillating frame 57K oscillates about the support shaft 501 as a fulcrum, moves to the retracted position, and stops there, as shown by the dashed arrow in Fig. 6(B). At this time, the oscillating frame 57K receives a spring force F1k due to the compression of the compression coil spring 59k, as shown in Fig. 6(B). As a result, the primary transfer roll 25K supported by the oscillating frame 57K moved to the retracted position keeps the intermediate transfer belt 31 in a retracted state away from the photosensitive drum 21 of the imaging unit 20K, as shown in Figure 6 (B).

[0104] As a result, when the lever 95 is operated to remain in the attachment / detachment position, the intermediate transfer unit 30 is in a state in which the intermediate transfer belt 31 is separated from all of the photosensitive drums 21 of the four imaging units 20 (Y, M, C, K) as shown in Fig. 6(B). The portion of the intermediate transfer belt 31 that is separated at this time is the portion 31t that corresponds to the portion 31j when forming the primary transfer surface. This allows the intermediate transfer unit 30 to be attached to and detached from the mounting portion 16 while avoiding unnecessary contact with the photosensitive drum 21 and the like.

[0105] 3, the intermediate transfer unit 30 is provided with two positioning guide pins 508 and 509 on the outer side of the rear support frame 50R so as to protrude toward the rear side. The positioning guide pin 509 is attached to one end of the support shaft 56, for example. Correspondingly, the mounting portion 16 of the housing 10 of the image forming apparatus 1 is provided at corresponding positions with two positioning receiving holes 18 and 19 into which the positioning guide pins 508 and 509 are inserted, respectively, as shown in FIG.

[0106] Therefore, when the intermediate transfer unit 30 is mounted in the mounting section 16, the positioning guide pins 508, 509 are inserted into the positioning receiving holes 18, 19 in the mounting section 16. As a result, the intermediate transfer unit 30 is positioned mainly by its support frames 50F, 50R with respect to the position where it should be mounted in the mounting section 16.

[0107] Furthermore, when the intermediate transfer unit 30 is mounted and positioned in the mounting portion 16, the passive side shaft coupling 39 of the belt support roll 32 is connected in a fitted state to the drive side shaft coupling 63 on the housing 10 side (see FIG. 2). The drive side shaft coupling 63 is a shaft coupling in the drive transmission section 62 of the drive device 6 arranged on the housing 10 side.

[0108] (3-1) Configuration of the mode switching device As shown in FIGS. 2, 8, 9, etc., the image forming apparatus 1 is provided, inside the rear side of the housing 10, with a mode switching device 7 that operates in conjunction with switching between the color mode and the black and white mode. Fig. 8(A) shows the state of the mode switching device 7 in the color mode, and Fig. 8(B) shows the state of the mode switching device 7 in the black and white mode.

[0109] The mode switching device 7 is a device that switches the primary transfer rolls 25Y, 25M, and 25C in the intermediate transfer unit 30 to either the transfer position or the retreat position in response to switching between the color mode and the black-and-white mode. The transfer positions of the primary transfer rolls 25Y, 25M, and 25C are positions when the oscillating frames 57Y, 57M, and 57C are oscillated to the above-mentioned operating positions. The retreat positions of the primary transfer rolls 25Y, 25M, and 25C are positions when the oscillating frames 57Y, 57M, and 57C are oscillated to the above-mentioned retreat positions.

[0110] 2 and other drawings, the mode switching device 7 is made up of a drive transmission unit 70 that transmits power to the first camshaft 53, and a power switching unit 80 that switches and transmits power to the drive transmission unit 70. A part of the drive transmission unit 70 and the power switching unit 80 are actually disposed inside a housing 81 shown in FIG. In addition, the mode switching device 7 is a device that essentially includes the front and rear movable frames 51F, 51R, the front and rear first cams 52F, 52R, the first cam shaft 53, the front and rear oscillating frames 57Y, 57M, 57C, 57H, etc. in the intermediate transfer unit 30.

[0111] As shown in FIGS. 8 to 10, the drive transmission section 70 includes a drive transmission shaft 71, a drive side shaft coupling 73, a moving transmission body 76, a biasing member 78, and the like.

[0112] The drive transmission shaft 71 is rotatably disposed in a housing 81 of the mode switching device 7 . The drive transmission shaft 71 receives power in different directions from the power switching unit 80 when switching between the color mode and the black and white mode, and rotates in different predetermined directions.

[0113] In addition, a passive gear 72 that receives the power transmitted from a power switching unit 80 is fixed to a part of the drive transmission shaft 71 . The passive gear 72 is provided on the outer circumferential surface of one open end of the cylindrical mounting support portion 723. Moreover, the passive gear 72 is attached to the drive transmission shaft 71 by fitting one end of the drive transmission shaft 71 into the internal space of the mounting support portion 723.

[0114] The drive-side shaft coupling 73 is a shaft coupling that is fitted and connected to the cam-side shaft coupling 54 of the intermediate transfer unit 30 . The drive-side shaft coupling 73 is attached to an end of the drive transmission shaft 71 opposite to the end to which the passive gear 72 is attached. More specifically, the drive-side shaft coupling 73 is attached in a fixed state with respect to the circumferential direction (rotational direction) of the drive transmission shaft 71 and in a movable state with respect to the axial direction.

[0115] As shown in Figs. 9(A) and 10, the drive-side shaft coupling 73 has a cylindrical main body 73a with one open end, and a fitted portion 74 is provided on a part of the main body 73a. As shown in FIG. 10, the driving side shaft coupling 73 has gear teeth 73g for transmitting power provided on the outer circumferential surface of its cylindrical main body 73a.

[0116] The fitted portion 74 is a portion into which the fitting portion 55 of the cam side shaft coupling 54 is fitted. The fitted portion 74 in the first embodiment is configured as a notched groove provided in a part of the opening of the cylindrical main body 73a. The notch groove of the fitted portion 74 is a recess cut out from a part of the opening of the main body 73a to extend linearly in the axial direction toward the rear with a predetermined width. The notch groove is formed with a width that allows the fitting portion 55 formed of the protrusion of the cam-side coupling 54 to be fitted in the axial direction of the drive transmission shaft 71.

[0117] The fitted portion 74 is fitted with the fitting portion 55 of the cam side shaft coupling 54 by the fitting portion 55 being fitted therein along the axial direction. However, the fitting portion 55 and the fitted portion 74 can be fitted to each other only when the phases in the rotational direction of the first camshaft 53 and the drive transmission shaft 71 are substantially aligned.

[0118] Furthermore, as shown in FIG. 9(A) and FIG. 10, the drive-side shaft coupling 73 is biased forward with a predetermined pressure by a compression coil spring 75. As a result, when the drive-side shaft coupling 73 is fitted and connected to the cam-side shaft coupling 54, it is elastically pressed toward the cam-side shaft coupling 54 by the spring force of the compression coil spring 75. This stabilizes the connection state of the drive-side shaft coupling 73 with the cam-side shaft coupling 54.

[0119] The moving transmission body 76 is a structure that meshes with the driven gear 72 of the drive transmission shaft 71 and moves within a certain range to transmit power. The moving transmission body 76 includes a moving main body 76a, a guide hole 76b, a rack gear 77, and the like.

[0120] The moving body 76a is a structure having a long shape in the vertical direction. The movable main body 76a is provided at its lower portion with an operating portion (not shown) for switching the operation corresponding to the mode switching of other components in the image forming unit 2.

[0121] The guide hole 76b is a long and narrow through hole formed in the upper part of the movable body 76a so as to extend linearly with a predetermined width substantially along the vertical direction. The guide hole 76b is supported and guided by upper and lower guide pins (bosses) 812, 813 provided on the housing 81. The guide pins 812, 813 are provided to protrude rearward in the housing 81. The guide pins 812, 813 are provided at positions spaced apart by a certain distance in the vertical direction in order to regulate the movement range of the movement transmitter 76, actually the movement range of the guide hole 76b.

[0122] The rack gear 77 is formed on one outer surface of the guide hole 76b in the left-right direction. The rack gear 77 is configured as a stepped two-row rack gear having a first rack gear 77a, a second rack gear 77b, and a third rack gear 77c.

[0123] The first rack gear 77a is a rack gear having a predetermined number of teeth formed in a front portion of the outer surface on one side of the guide hole 76b, in a portion corresponding to the upper side of the guide hole 76b. The first rack gear 77a is disposed so as to be able to mesh with a transmission gear 86, which will be described later.

[0124] The second rack gear 77b is a rack gear with a predetermined number of teeth formed in a rear portion of the outer surface on one side of the guide hole 76b at a position corresponding to the upper side of the guide hole 76b and one step higher than the first rack gear 77a. In this case, the one step higher position refers to a position that is farther away from the guide hole 76b. The second rack gear 77b is disposed adjacent to and overlapping with the first rack gear 77a in the front-rear direction. Furthermore, the second rack gear 77b is disposed in a state shifted upward with respect to the first rack gear 77a. The second rack gear 77b is disposed so as to be able to mesh with a second gear portion 85B of a transmission gear 85, which will be described later.

[0125] The third rack gear 77c is a rack gear having a predetermined number of teeth formed on a lower side than the second rack gear 77b in a rear portion on one side of the outside of the guide hole 76b. The third rack gear 77c is disposed so as to be constantly in mesh with the driven gear 72 of the drive transmission shaft 71.

[0126] The movement transmission body 76 moves up and down within a predetermined range in the vertical direction while the guide hole 76b is guided by guide pins 812, 813 arranged at intervals in the vertical direction. Furthermore, a part of the moving transmission body 76 is detected by a position detection sensor 79, and the position when it moves up and down is grasped.

[0127] The biasing member 78 biases the drive transmission shaft 71 in a rotatable direction when the fitting portion 55 of the cam side shaft coupling 54 and the fitted portion 74 of the drive side shaft coupling 73 are not fitted to each other.

[0128] In the first embodiment, a tension coil spring is used as the biasing member 78. 9(B) and other figures, the tension coil spring serving as the urging member 78 is attached by hooking one end (upper end) onto a part of the passive gear 72. The part of the passive gear 72 is, for example, an attachment protrusion 724 provided on an end face of an attachment support portion 723 of the passive gear 72. Moreover, the tension coil spring serving as the biasing member 78 is attached by having the other end (lower end) hooked onto an attachment portion 81b provided on the housing 81.

[0129] The biasing member 78 is positioned in a state in which it biases the drive transmission shaft 71, which rotates and then stops when switching to the color mode, to rotate it further in the direction in which it was rotating to the extent possible (see FIG. 11(B)). In addition, the biasing member 78 is positioned in a state in which it biases the drive transmission shaft 71, which rotates and then stops when the mode is switched to black and white, so as to rotate it further in the direction in which it was rotating to the extent possible (see FIG. 12(B)).

[0130] In order to realize such a biasing force, the biasing member 78 is disposed so that the other end (lower end) is located below the drive transmission shaft 71. At this time, the biasing member 78 is disposed so that one end (upper end) thereof is present at a position shifted to a different side from the uppermost point (or shaft center) of the drive transmission shaft 71 at which each of the rotations has stopped. Furthermore, the biasing members 78 at this time are arranged such that their one ends (upper ends) are located at positions shifted to different sides within a region corresponding to the upper half of the drive transmission shaft 71.

[0131] The mounting support portion 723 of the passive gear 72 is a cylindrical portion protruding rearward of the passive gear 72. One end of the drive transmission shaft 71 is fitted into the internal space of the mounting support portion 723, thereby mounting the passive gear 72 to the drive transmission shaft 71. The mounting protrusion 724 is provided so as to protrude from an eccentric position at the end of the mounting support portion 723. The biasing member 78 biases the passive gear 72 and therefore the drive transmission shaft 71 to rotate in different directions depending on the different positions at which the drive transmission shaft 71 and therefore the passive gear 72 stop about the center of rotation of the drive transmission shaft 71 and therefore the passive gear 72 (see Figures 11(B) and 12(B)).

[0132] Next, as shown in Figures 8 to 10, the power switching unit 80 includes a drive motor 82, an upstream transmission gear 83, a toothless gear 84, downstream transmission gears 85 and 86, a swing hook arm 87, a torsion spring 88, and the like.

[0133] The drive motor 82 has a gear attached to an output shaft 82b that rotates in a predetermined direction. The upstream transmission gear 83 employs three gears, a first transmission gear 83A, a second transmission gear 83B, and a third transmission gear 83C. The first transmission gear 83A, the second transmission gear 83B, and the third transmission gear 83C are two-stage gears consisting of a small diameter portion and a large diameter portion, and form a reduction gear train.

[0134] The toothless gear 84 intermittently transmits power from the upstream transmission gear 83 to the downstream transmission gears 85 and 86 . The toothless gear 84 has a shaft attachment portion 84a that is rotatably attached to a support shaft (not shown), and a cylindrical large diameter portion 84b and a small diameter portion 84c that are provided on the outside of the shaft attachment portion 84a.

[0135] The large diameter portion 84b is formed with a first tooth-missing gear portion 841 and a second tooth-missing gear portion 842 sandwiching two tooth-missing (vacant) portions therebetween. Both the first tooth-missing gear portion 841 and the second tooth-missing gear portion 842 are configured as special gears that are divided into an upstream gear portion and a downstream gear portion with some of them overlapping and shifted in the axial direction in the circumferential direction of the large diameter portion 84b, as shown in Figure 9. In this case, the downstream gear portion of the first toothless gear portion 841 is disposed to mesh with a second gear portion 85B (described later) of the downstream transmission gear 85. The downstream gear portion of the second toothless gear portion 842 is disposed to mesh with a first gear portion 85A (described later) of the downstream transmission gear 85.

[0136] The small diameter portion 84c is provided with a hook portion 845 that hooks the hook portion of the swing hook arm 87 to stop the rotation of the tooth-missing gear 84. The hook portions 845 are provided at two locations 180° apart in the circumferential direction of the small diameter portion 84c.

[0137] When the hook portion of the swing hook arm 87 is hooked on the hook portion 845, the toothless gear 84 is set so that its toothless portion faces the third transmission gear 83C, as shown in Fig. 9(A) etc. This places the toothless gear 84 in a state where neither the first toothless gear portion 841 nor the second toothless gear portion 842 meshes with the third transmission gear 83C. The tooth-missing gear 84 starts to rotate by receiving the spring force of the torsion spring 88 when the hook portion of the swinging hook arm 87 is released from the hook portion 845. The tooth-missing gear 84 stops rotating when the hook portion of the swinging hook arm 87 is hooked on the next hook portion 845 half a revolution away.

[0138] The swinging hook arm 87 is a member that swings so that the hook portion at the tip of the arm approaches and moves away from the small diameter portion 84c. The swinging hook arm 87 is swung in a direction away from the small diameter portion 84c by the driving force of the solenoid 89. When the solenoid 89 is not activated, the swinging hook arm 87 is biased by a biasing member (not shown) so as to swing in a direction approaching the small diameter portion 84c.

[0139] As shown in FIG. 9B, the toothless gear 84 has a spring bearing portion 847 provided between the internal space of the small diameter portion 84c and the shaft attachment portion. The spring bearing portion 847 is a plate-shaped portion extending in the diameter direction of the shaft attachment portion 84a. The spring bearing portion 847 receives the spring force with which the arm portion of the torsion spring 88 comes into contact and rotates the chipped gear 84 in a fixed direction. Torsion spring 88 is attached such that an arm extending from its coil portion is kept in contact with spring receiving portion 847, and the coil portion is held by spring holding portion 881. Spring holding portion 881 is attached to a part of housing 81.

[0140] When the hook portion of the swing hook arm 87 is released from the hook portion 845, the toothless gear 84 is caused to rotate in the clockwise direction in Fig. 8 by the spring force of the torsion spring 88. As a result, the toothless gear 84 is configured so that the first toothless gear portion 841 and the second toothless gear portion 842 individually mesh with the third transmission gear 83C.

[0141] The downstream transmission gear 85 is composed of a first gear portion 85A and a second gear portion 85B serving as idle gears rotatable about the same shaft. The first gear portion 85A is disposed so as to mesh with the downstream transmission gear 86. The second gear portion 85B is disposed so as to be able to mesh with the second rack gear 77b of the moving transmission body 76. The downstream transmission gear 86 is disposed so as to mesh with a first gear portion 85A of the downstream transmission gear 85. In addition, the downstream transmission gear 86 is disposed so as to be able to mesh with a first rack gear 77a of the moving transmission body 76.

[0142] (3-2) Operation of the mode switching device (3-2-1) Switching from black and white to color mode When the mode switching device 7 is switched from the black and white mode to the color mode, it operates as follows.

[0143] At this time, the mode switching device 7 temporarily activates the solenoid 89 in the power switching section 80 under the control of a control device (not shown). At this time, the solenoid 89 operates to swing the swing hook arm 87 in a direction in which the hook portion is disengaged from the catch portion 845 of the tooth-missing gear 84 . As a result, the toothless gear 84 receives the spring force of the torsion spring 88 and is rotated counterclockwise in FIG. Furthermore, the upstream gear portion of the first tooth-missing gear portion 841 of this rotating tooth-missing gear 84 begins to mesh with (the gear of the small diameter portion of) the third transmission gear 83C.

[0144] At this time, the mode switching device 7 operates the drive motor 82 of the power switching unit 80 in accordance with the above operation. At this time, the drive motor 82 drives the third transmission gear 83C to rotate in the clockwise direction in FIG. 8(A). As a result, the tooth-missing gear 84 receives power from the third transmission gear 83C at the first tooth-missing gear portion 841 and rotates in the counterclockwise direction. Further, in this rotating tooth-missing gear 84, the downstream gear portion of the second tooth-missing gear portion 842 meshes with the second gear portion 85B of the transmission gear 85 on the downstream side. As a result, the tooth-missing gear 84 rotates the second gear portion 85B in the clockwise direction in FIG. 8(A).

[0145] At this time, the second gear portion 85B rotates by an amount corresponding to the meshing with the teeth of the downstream gear portion of the second toothless gear portion 842. At this time, the tooth-missing gear 84 stops rotating as the hook portion of the swing hook arm 87 gets caught on the next hook portion 845 located half a revolution away.

[0146] Subsequently, the second gear portion 85B rotating in the clockwise direction meshes with the second rack gear 77b of the moving transmission body 76 to transmit power. As a result, the moving transmission body 76 is moved downward as shown by the dashed arrow in Fig. 8(A) At this time, the moving transmission body 76 is moved downward a predetermined distance by the amount of rotation of the second gear portion 85B meshing with the second rack gear 77b.

[0147] At this time, as shown in FIG. 8(A), when the intermediate transfer unit 30 is attached, the movable transmission body 76 is set so that, in principle, the upper end portion 76p of the guide hole 76b stops at a position just before approaching the upper guide pin 812. Also, at this time, the second gear portion 85B is released from meshing with the second rack gear 77b of the moving transmission body 76, and then released from meshing with the second tooth-missing gear portion 842 of the tooth-missing gear 84.

[0148] Next, when the moving transmission body 76 moves downward a predetermined distance, the passive gear 72 meshing with the third rack gear 77c of the moving transmission body 76 is rotated a predetermined angle in the clockwise direction in FIG. 8(A). 8 is transmitted from the drive-side shaft coupling 73 to the first camshaft 53 via the cam-side shaft coupling 54. This causes the first camshaft 53 to rotate in the same direction as the drive transmission shaft 71.

[0149] Next, in the intermediate transfer unit 30, the rotation of the first cam shaft 53 causes the front and rear first cams 52F, 52R to rotate by a predetermined angle in the clockwise direction in FIG. 5(A). At this time, the first cams 52F, 52R are in a state in which the cam action portions 52a thereof are moved in a direction away from the cam contact surfaces 515 of the front and rear moving frames 51F, 51R. The predetermined angle at this time is, for example, an angle of 180° from the stop positions of the first cams 52F, 52R in the black and white mode. As a result, the front and rear movable frames 51F, 51R are not subjected to the action of the first cams 52F, 52R, but instead receive the biasing force in the direction of arrow D1 from each spring as described above, and move in the direction indicated by arrow D1.

[0150] Finally, in the intermediate transfer unit 30, the swing frames 57Y, 57M, and 57C are biased by the compression coil springs 59y, 59m, and 59c to swing to their respective operating positions, respectively, while the swing frame 57H in the intermediate transfer unit 30 is biased by the tension coil spring 59h to swing to its operating position. As a result, the primary transfer rolls 25Y, 25M, and 25C and the belt support roll 34 move to the transfer position or the operating position, respectively.

[0151] As a result, in the intermediate transfer unit 30, as shown in FIG. 5, a part 31j of the intermediate transfer belt 31 forms a primary transfer surface and is in contact with each of the photosensitive drums 21 of the imaging units 20Y, 20M, and 20C. When the above operations are completed, the image forming apparatus 1 becomes capable of performing image forming operations in the color mode.

[0152] (3-2-2) Switching from color mode to black and white mode Moreover, when the color mode is switched to the black and white mode, the mode switching device 7 operates as follows.

[0153] At this time, in the mode switching device 7, the solenoid 89 in the power switching section 80 is temporarily operated by a control device (not shown), in the same manner as when switching to the color mode. By the operation of the solenoid 89, the hook portion of the swing hook arm 87 is disengaged from the catch portion 845 of the tooth-missing gear 84. As a result, the tooth-missing gear 84 receives the spring force of the torsion spring 88 and is rotated clockwise in FIG. Furthermore, the second tooth-missing gear portion 842 of this rotating tooth-missing gear 84 begins to mesh with (the gear of the small diameter portion of) the third transmission gear 83C.

[0154] At this time, the mode switching device 7 operates the drive motor 82 of the power switching unit 80 in accordance with the above operation. At this time, the drive motor 82 drives the third transmission gear 83C to rotate in the clockwise direction in FIG. 8(A). As a result, the tooth-missing gear 84 receives power from the third transmission gear 83C and rotates counterclockwise. At this time, the downstream gear portion of the first tooth-missing gear portion 841 of the tooth-missing gear 84 meshes with the first gear portion 85A of the downstream transmission gear 85. Furthermore, the rotating tooth-missing gear 84 rotates the first gear portion 85A in the clockwise direction in FIG. 8(B).

[0155] At this time, the first gear portion 85A rotates by an amount corresponding to the meshing with the teeth of the downstream gear portion of the first toothless gear portion 841. At this time, the tooth-missing gear 84 stops rotating as the hook portion of the swing hook arm 87 gets caught on the next hook portion 845 located half a revolution away.

[0156] Next, the first gear portion 85A rotating in the clockwise direction rotates the downstream transmission gear 86 with which it meshes in the counterclockwise direction. At this time, the downstream transmission gear 86 transmits power to the first rack gear 77a of the moving transmission body 76, moving the moving transmission body 76 upward. At this time, the downstream transmission gear 86 also rotates by the amount that the first gear portion 85A of the moving transmission body 76 rotates in mesh with the first rack gear 77a, and the moving transmission body 76 is moved upward a predetermined distance.

[0157] At this time, as shown in FIG. 8(B), when the intermediate transfer unit 30 is attached, the movable transmission body 76 is set so that, in principle, the lower end portion 76q of the guide hole 76b stops at a position just before approaching the lower guide pin 813. Also, at this time, the first gear portion 85A is also released from meshing with the first tooth-missing gear portion 841 of the tooth-missing gear 84 after the downstream transmission gear 86 is released from meshing with the first rack gear 77a of the moving transmission body 76.

[0158] Next, when the moving transmission body 76 moves upward by a predetermined distance, the passive gear 72 meshing with the third rack gear 77c of the moving transmission body 76 is rotated by a predetermined angle in the counterclockwise direction in FIG. 8(B). 8(B) is transmitted from the drive-side shaft coupling 73 to the first camshaft 53 via the cam-side shaft coupling 54. This causes the first camshaft 53 to rotate in the same direction as the drive-transmission shaft 71.

[0159] Next, in the intermediate transfer unit 30, the rotation of the first cam shaft 53 causes the front and rear first cams 52F, 52R to rotate counterclockwise in FIG. 6A by a predetermined angle. At this time, the first cams 52F, 52R are in a state in which the cam action portions 52a are moved in a direction in which they come into contact with the cam contact surfaces 515 of the front and rear moving frames 51F, 51R. The predetermined angle at this time is, for example, an angle of 180° from the stop positions of the first cams 52F, 52R in the color mode. As a result, the front and rear moving frames 51F, 51R are moved in the direction indicated by the arrow D2 by the action of the first cams 52F, 52R.

[0160] Finally, in the intermediate transfer unit 30, the oscillating frames 57Y, 57M, 57C, and 57H are pushed in the directions indicated by arrows D2 by the pushing portions 58y, 58m, 58c, and 58h of the moving frames 51F and 51R, respectively, and oscillate to their respective retreat positions. As a result, the primary transfer rolls 25Y, 25M, and 25C and the belt support roll 34 move to the transfer position or the operating position, respectively. When the oscillating frame 57 is oscillated to the retracted position, the compression coil springs 59y, 59m, and 59c of the oscillating frames 57Y, 57M, and 57C are compressed, and the tension coil spring 59h of the oscillating frame 57H is extended.

[0161] As a result, in the intermediate transfer unit 30, as shown in FIG. 6A, a portion 31s of the intermediate transfer belt 31 does not form a primary transfer surface and is separated from each of the photosensitive drums 21 of the imaging units 20Y, 20M, and 20C. When the above operations are completed, the image forming apparatus 1 becomes capable of performing image forming operations in the black and white mode.

[0162] (3-3) State and operation of intermediate transfer unit 30 during installation and removal When the intermediate transfer unit 30 is attached or detached, it may be in a state switched to a color mode or in a state switched to a black and white mode.

[0163] In either case, when the intermediate transfer unit 30 is attached or detached, the image forming apparatus 1 makes it easy to fit the cam side shaft joint 54 and the drive side shaft joint 73 together when the intermediate transfer unit 30 is attached. When the intermediate transfer unit 30 is removed from the mounting portion 16 of the image forming apparatus 1, the cam-side shaft coupling 54 is separated from the drive-side shaft coupling 73 of the mode switching device 7 and becomes free (see FIG. 10).

[0164] (3-3-1) When the intermediate transfer unit 30 in the color mode is removed First, a case where the intermediate transfer unit 30 in the color mode is removed will be described. In this case, as shown in FIG. 11, the upper end of the biasing member 78 in the mode switching device 7 moves to a position closer to the movable transmission body 76 than the axis of the drive transmission shaft 71 and above the axis, and stops there. At this time, the axis of the drive transmission shaft 71 coincides with the center of the circular end face portion of the mounting support portion 723 of the passive gear 72 in the first embodiment.

[0165] As a result, the tension coil spring of the biasing member 78 biases the mounting protrusion 724 to which its upper end is attached, downward with spring force F1 toward its lower end at an eccentric position closer to the moving transmission body 76 than the axis of the drive transmission shaft 71. The biasing force of the biasing member 78 causes the driven gear 72 to rotate slightly in the clockwise direction in FIG. 11(A) (counterclockwise direction in FIG. 11(B)).

[0166] As a result, the movable transmission body 76 in the mode switching device 7 is moved slightly downward by the third rack gear 77c receiving the power of the passive gear 72 which rotates slightly in the clockwise direction. At this time, the movable transmission body 76 moves to a position where the upper end portion 76p of the guide hole 76b contacts the upper guide pin 812 and stops, as shown in FIG.

[0167] As a result, the driving side shaft coupling 73 in the mode switching device 7 is biased by the biasing member 78. Therefore, the movable range of the driving side shaft coupling 73 at this time is expanded to a movable position P1 which is larger than the normal movable range of the driving side shaft coupling 73 when the intermediate transfer unit 30 in the color mode is attached as shown in FIG. The position of the above-mentioned principle range of motion of the drive side shaft coupling 73 in the color mode state is the position when the upper end portion 76p of the guide hole 76b in the movable transmission body 76 stops at a position just before approaching the upper guide pin 812, as shown in Figure 8 (A).

[0168] Moreover, the increased range of motion of the drive-side shaft joint 73 at this time exceeds the range of motion of the cam-side shaft joint 54 in the intermediate transfer unit 30 when it is removed, as shown in FIG. At this time, the cam-side shaft coupling 54 is not biased in any way in the direction in which the first camshaft 53 and the first cams 52F, 52R can rotate, and is therefore in a state in which it does not move in the rotating direction.

[0169] As a result, the range of motion of the drive-side shaft joint 73 is wider than the range of motion of the cam-side shaft joint 54 even when in the color mode. This also makes it possible to fine-tune the position of the mating portion 74 of the drive side shaft coupling 73 when the intermediate transfer unit 30 in color mode is mounted in the mounting portion 16, making it easier to align the mating portion 74 with the phase of the mating portion 55 of the cam side shaft coupling 54.

[0170] Therefore, in the image forming device 1, even when the intermediate transfer unit 30 in the color mode is attached to the attachment portion 16, it is easy to engage the engaging portion 55 of the cam side shaft coupling 54 and the engaged portion 74 of the drive side shaft coupling 73 with each other.

[0171] (3-3-2) When the intermediate transfer unit 30 in the black-and-white mode is removed Next, a case where the intermediate transfer unit 30 in the black and white mode is removed will be described. In this case, as shown in FIG. 12, the upper end of the biasing member 78 in the mode switching device 7 moves to a position farther from the movable transmission body 76 than the drive transmission shaft 71 and above the axis, and stops there.

[0172] As a result, the tension coil spring of the biasing member 78 biases the mounting protrusion 724, to which the upper end of the spring is attached, downward with a spring force F2. The bias at this time is such that the mounting protrusion 724 is pulled toward the lower end of the spring at a position eccentric to the side opposite the moving transmission body 76 from the axis of the drive transmission shaft 71. The biasing force of the biasing member 78 causes the driven gear 72 to rotate slightly in the counterclockwise direction in FIG. 12(A) (clockwise direction in FIG. 12(B)).

[0173] As a result, the movable transmission body 76 in the mode switching device 7 is moved upward by the third rack gear 77c receiving the power of the passive gear 72 rotating in the counterclockwise direction. At this time, the movable transmission body 76 moves to a position where the lower end portion 76q of the guide hole 76b contacts the lower guide pin 813 and stops, as shown in Fig. 12.

[0174] As a result, the driving-side shaft coupling 73 in the mode switching device 7 is biased by the biasing member 78. Therefore, the movable range of the driving-side shaft coupling 73 at this time is expanded to a movable position P2 which is larger than the basic movable range when the intermediate transfer unit 30 in the black-and-white mode is attached as shown in FIG. The position of the movable range of the drive side shaft coupling 73 according to the above principle in the black and white mode state is the position when the lower end portion 76q of the guide hole 76 in the movable transmission body 76 stops at a position just before approaching the lower guide pin 813, as shown in Figure 8 (B).

[0175] Moreover, the increased range of motion of the drive-side shaft joint 73 at this time exceeds the range of motion of the cam-side shaft joint 54 in the intermediate transfer unit 30 when it is removed, as shown in FIG. As a result, the movable range of the drive-side shaft joint 73 is wider than the movable range of the cam-side shaft joint 54 even when in the monochrome mode. This also enables fine adjustment of the position of the fitted portion 74 of the drive-side shaft coupling 73 when the intermediate transfer unit 30 in the black-and-white mode is mounted in the mounting portion 16. As a result, the fitted portion 74 of the drive-side shaft coupling 73 can be easily aligned with the phase of the fitting portion 55 of the cam-side shaft coupling 54.

[0176] Therefore, in the image forming device 1, even when the intermediate transfer unit 30 in the black and white mode is attached to the attachment portion 16, it is easy to engage the engaging portion 55 of the cam side shaft coupling 54 and the engaged portion 74 of the drive side shaft coupling 73 with each other.

[0177] (3-4) Configuration and defects of the intermediate transfer unit to be compared In contrast, when the configuration of the intermediate transfer unit 30X for comparison shown in FIGS. 14 and 15 is adopted, the following problem occurs.

[0178] First, the intermediate transfer unit 30X for comparison differs in that instead of providing the above-mentioned urging member 78 on the housing 10 side of the image forming device 1, a urging member 780 is provided on the intermediate transfer unit 30X side, but otherwise has a configuration substantially the same as that of the intermediate transfer unit 30. In the intermediate transfer unit 30X for comparison, a biasing member 780 is provided as a biasing member that biases the first cam 52X in a rotatable direction. The biasing member 780 is a torsion spring.

[0179] The torsion spring which is the biasing member 780 has its coil portion 781 fitted from the outside into a cylindrical spring holding portion 528 which is attached to the first cam shaft 53 of the first cam 52X by passing through the spring holding portion 528. Further, the torsion spring which is the biasing member 780 has two arm portions 782, 783 extending in two directions from a coil portion 781 in a V-shape and held by a pair of spring holding portions 527, 528 provided on the side surface of the first cam 52X. The pair of spring holding portions 527, 528 are portions which are shaped so as to surround the two arm portions 782, 783 with openings on the inner sides facing each other.

[0180] The two arm portions 782, 783 are accommodated in a pair of spring holding portions 527, 528 from their respective inner sides and held in a displaceable manner. Further, the two arm portions 782, 783 each have a ring-shaped winding portion formed at its tip, and each winding portion is disposed in a state where it protrudes to the outside of the first cam 52X.

[0181] When the comparative intermediate transfer unit 30X is removed in color mode, as shown in Figure 14(A), the first cam 52X is positioned with its cam action portion 52a positioned almost on the opposite side of the first cam shaft 53 from the cam contact surface 515. When switching to the color mode, the first cam 52X receives power from the mode switching device 7 (not shown) and rotates counterclockwise in FIG. 14A, similar to the case of the intermediate transfer unit 30 in the first embodiment.

[0182] At this time, as shown in FIG. 14B, the first cam 52X of the intermediate transfer unit 30X may rotate to the maximum movable position when the color mode is switched. At this time, the first cam 52X stops when the protruding first rotation stopper 525 on the outer periphery hits the bottom surface 514b of the cam accommodating part. Also at this time, one arm portion (wound portion) 782 of the torsion spring which is the biasing member 780 comes into contact with the bottom surface 514b of the cam accommodating part and elastically deforms so as to be displaced inward within the spring holding part 527. 14(B), the first cam 52X receives a spring force F11 in the clockwise direction in the figure from the other arm portion 783 of the torsion spring which is the biasing member 780. This causes the first cam 52X to rotate slightly back in the clockwise direction in FIG. 14(B) due to the spring force F11 of the biasing member 780.

[0183] In this way, in the comparative intermediate transfer unit 30X, even if the first cam 52X rotates to the maximum movable position when it is removed in the color mode, it rotates slightly back due to the biasing force of the biasing member 780. Moreover, the same situation also applies to the movable range of the cam-side shaft coupling 54 fixed to the first cam shaft 53 to which the first cam 52X is attached.

[0184] Therefore, when the comparative intermediate transfer unit 30X is removed in the color mode, as shown in FIG. 16, even if the cam side shaft coupling 54 rotates to the maximum movable position through the rotation of the first cam 52X, it is corrected to the movable position X1. The correction at this time is performed by the cam-side shaft coupling 54 receiving the biasing force of the biasing member 780 via the first cam 52X. Further, the corrected movable position X1 of the cam side shaft coupling 54 at this time is set to be a position inside the movable range of the drive side shaft coupling 73 in the color mode.

[0185] Furthermore, when the comparative intermediate transfer unit 30X is removed in the black-and-white mode, the first cam 52X brings the cam action portion 52a into contact with the cam contact surface 515 as shown in FIG. 15(A). When switching to the black-and-white mode, the first cam 52X receives power from the mode switching device 7 (not shown) and rotates in the clockwise direction in FIG. 15A, similar to the case of the intermediate transfer unit 30 in the first embodiment.

[0186] In addition, in the intermediate transfer unit 30X at this time, as shown in FIG. 15B, the first cam 52X may rotate to the maximum movable position when switching to the black-and-white mode. At this time, the first cam 52X stops as the protruding second rotation stopper 526 on the outer periphery of the first cam 52X comes into contact with the bottom surface 514b of the cam accommodating portion. At this time, the other arm portion (wound portion) 783 of the torsion spring which is the biasing member 780 comes into contact with the bottom surface 514b of the cam accommodating portion and elastically deforms so as to move inward within the spring holding portion 528. As a result, as shown in Fig. 15(B), the first cam 52X receives a spring force F21 in the counterclockwise direction in the figure from one arm portion 782 of the torsion spring which is the biasing member 780. This causes the first cam 52X to rotate slightly back in the counterclockwise direction in Fig. 15(B) due to the spring force F21 of the biasing member 780.

[0187] Thus, in the comparative intermediate transfer unit 30X, even if the first cam 52X rotates to its maximum movable position when it is removed in the black and white mode, it is rotated back slightly by the force of the biasing member 780. In the intermediate transfer unit 30X, as shown in FIG. 15(A), even when the first cam 52X does not rotate to the maximum movable position and remains in the position at the end of switching to the black-and-white mode, it can rotate slightly back due to the biasing force (spring force F21) of the biasing member 780. Moreover, this situation also applies to the movable range of the cam-side shaft coupling 54 as described above.

[0188] Therefore, when the comparative intermediate transfer unit 30X is removed in the black and white mode as shown in FIG. 16, even if the cam side shaft coupling 54 rotates to the maximum movable position through the rotation of the first cam 52X, it is corrected to the movable position X2. The correction at this time is performed by the cam-side shaft coupling 54 receiving the biasing force of the biasing member 780 via the first cam 52X. Further, the corrected movable position X2 of the cam side shaft joint 54 at this time is set to be a position inside the movable range of the drive side shaft joint 73 in the monochrome mode.

[0189] However, when the intermediate transfer unit 30X for comparison is removed, particularly in the black-and-white mode, the first cam 52X keeps its cam action portion 52a in contact with the cam contact surface 515 as shown in FIG. 15(A). For this reason, even if the first cam 52X receives the bias (spring force F21) of the biasing member 780, it is often unable to rotate so as to be returned slightly. Moreover, even when the first cam 52X has rotated to the maximum movable position at this time, the second rotation stopper 526 continues to contact the bottom surface portion 514b of the cam accommodating portion as shown in FIG. 15(B), so the same applies.

[0190] As a result, like the first cam 52X, the cam side joint 54 cannot rotate so as to be corrected by receiving the bias of the biasing member 780. In other words, the cam side joint 54 at this time is not corrected by the bias of the biasing member 780 in its movable range.

[0191] In this case, when attempting to mount the intermediate transfer unit 30X in the black and white mode in the mounting portion 16, the phase of the mating portion 55 of the cam side shaft coupling 54 in the intermediate transfer unit 30X and the mating portion 74 of the drive side shaft coupling 73 on the mode switching device 7 side do not match, or it is difficult to adjust the phase to match. Therefore, in this case, the intermediate transfer unit 30X has a problem that it is difficult to fit the fitting portion 55 of the cam side shaft coupling 54 into the fitted portion 74 of the drive side shaft coupling 73.

[0192] Also, the above fitting may be performed in an incomplete state, which may result in a malfunction in the transmission of power from the drive-side shaft coupling 73 to the cam-side shaft coupling 54 during image forming operations. More specifically, the corrected movable position X2 of the cam side coupling 54 is a position where the cam side coupling 54 is stopped at the maximum movable range. Therefore, even if the drive side coupling 73 rotates to the maximum movable range, the phases of the drive side coupling 73 and the drive side coupling 73 will not match, and there is a concern that the drive will not be transmitted.

[0193] In this regard, in the image forming apparatus 1 according to the first embodiment, the movable range of the drive transmission shaft 71 is easily corrected by being biased by the biasing member 78, compared to a comparative intermediate transfer unit 30X in which the biasing member 780 is provided on the intermediate transfer unit 30X side. As a result, it is easy to fit the cam side shaft coupling 54 and the drive side shaft coupling 73 when the intermediate transfer unit 30 is attached. In addition, in the image forming apparatus 1, when the intermediate transfer unit 30 in the color mode is mounted in the mounting portion 16, the cam side shaft coupling 54 and the drive side shaft coupling 73 can be easily fitted together in the same manner.

[0194] Incidentally, when the intermediate transfer unit 30X for comparison is removed in the black-and-white mode, this can be dealt with by operating a lever as shown in FIG. 15(B).

[0195] The lever operation at this time refers to an operation of tilting the lever 95 further in the direction indicated by the arrow M2 from the attachment / detachment position, thereby slightly moving the moving frame 51(F) in the direction indicated by the arrow D2. Moreover, the movable frame 51(F) moves slightly in the direction indicated by the arrow D2 by operating this lever due to the following mechanism. That is, in this lever operation, the lever 95 is swung in the direction indicated by the arrow M2 so as to be tilted further than usual. As a result, in the intermediate transfer unit 30X, as illustrated in Fig. 7, the protrusion 529 provided on the first cam 52 is brought into contact with the tip bent portion 513b of the protruding support portion 513 of the moving frame 51(F) from the inside in conjunction with the rotation of the second cam shaft 561. As a result, the moving frame 51(F) is further pushed in the direction indicated by the arrow D2 and is moved slightly.

[0196] By performing this lever operation, the movable frame 51(F) moves slightly in the direction indicated by the arrow D2, and the cam contact surface 515 also moves in the same manner. As a result, the first cam 52X is in a state in which its cam action portion 52a is separated from the cam contact surface 515, as shown in FIG. 15(B).

[0197] As a result, even in the black-and-white mode, the first cam 52X rotates and the movable position is corrected by receiving the bias (spring force F21) from the torsion spring that is the biasing member 780. That is, the movable range of the cam side coupling 54 in the intermediate transfer unit 30X at this time is also corrected by the bias of the biasing member 780. This also makes it easier to fit the cam-side shaft joint 54 and the drive-side shaft joint 73 together, even when the intermediate transfer unit 30X for comparison in the black-and-white mode is mounted in the mounting portion 16.

[0198] However, this lever operation must be performed against all of the spring forces F1y, F1m, F1c, and F1k (see FIG. 6B) of multiple compression coil springs 59y, 59m, 59c, and 59k that are also arranged in the intermediate transfer unit 30X. That is, in the comparative intermediate transfer unit 30X, a large operating force is required to operate the lever.

[0199] In this regard, in the image forming apparatus 1 according to the first embodiment, even when removing the intermediate transfer unit 30 in the black and white mode, there is no need to perform an extra lever operation as in the comparative intermediate transfer unit 30X, making it easy to handle.

[0200] Variations. The present invention is not limited to the configuration exemplified as the above-mentioned embodiment 1, and various modifications and alterations can be made without departing from the spirit of the inventions described in the claims. The present invention also includes, for example, the following modifications.

[0201] In the first embodiment, the intermediate transfer unit 30 has been described as an example, but the present invention can be applied between a removable unit other than the intermediate transfer unit and the housing 10 which is an example of the main body of the image forming apparatus 1.

[0202] In this case, the detachable unit may include a support frame detachably attached to the housing 10 of the image forming apparatus 1, a movable frame movably arranged relative to the support frame, a first cam that moves the movable frame, its cam shaft, a cam-side shaft coupling fixed to one end of the cam shaft, etc. Also, in this case, the detachable unit may include a drive transmission shaft to which a passive gear is fixed, a drive-side shaft coupling fixed to one end of the drive transmission shaft, a movable transmission body that meshes with the passive gear and moves within a certain range to transmit power, etc.

[0203] In addition, the biasing member 78 may be a member other than a tension coil spring, provided that it can bias the drive transmission shaft 71 in a rotatable direction when the mating portion 55 of the cam side shaft coupling 54 and the mated portion 74 of the drive side shaft coupling 73 are not mated. Further, instead of attaching one end of the urging member 78 to a part of the driven gear 72 of the drive transmission shaft 71 , a configuration in which the urging member 78 is attached to a part of the drive transmission shaft 71 may be adopted.

[0204] Furthermore, depending on conditions such as the setting of the load (spring force) and how it is applied, the biasing member 78 may be arranged so that one end (upper end) is located at a position shifted to a different side in the region corresponding to the lower half of the drive transmission shaft 71. However, the lower half does not include the lowest point of the drive transmission shaft 71 and the vicinity thereof, where the biasing force of the biasing member 78 is not exerted or is difficult to exert.

[0205] Furthermore, the cam side shaft coupling 54 and the fitting portion 55, and the drive side shaft coupling 73 and the fitted portion 74 may have configurations other than those exemplified in the first embodiment.

[0206] (Additional Note) (((1))) A main body having an image forming unit; A detachable unit having a support body that is detachably attached to the main body; A movable body that is movably disposed relative to the support and is biased in one direction; a cam that moves the moving body in a direction opposite to the one direction; a cam shaft rotatably disposed on the support and having the cam fixed thereto; a cam-side shaft coupling attached to one end of the camshaft and having a fitting portion; a drive transmission shaft rotatably disposed on the main body side and having a passive gear fixed thereto for receiving the power transmission; a drive-side shaft coupling attached to one end of the drive transmission shaft and having a fitted portion into which the fitting portion is fitted; a moving transmission body that is disposed on the main body side and meshes with the passive gear to move within a certain range to transmit power; a biasing member that is disposed on the main body side and biases the drive transmission shaft in a rotatable direction when the fitting portion and the fitted portion are not fitted to each other; An image forming apparatus comprising: (((2))) The image forming apparatus described in (((1))) wherein the urging member urges the drive side shaft coupling so that the range of motion of the drive side shaft coupling is wider than the range of motion of the cam side shaft coupling when the engaging portion and the engaged portion are not engaged. (((3))) The image forming apparatus according to (((1))) or (((2))), wherein the urging member is a tension spring having one end attached to a part of the main body and the other end attached to an eccentric part of the other end of the drive transmission shaft. (((4))) the removable unit is an intermediate transfer unit having an intermediate transfer belt that is rotated around a plurality of rotating rolls that are arranged on the support, and a plurality of primary transfer rolls that are arranged on the support and are urged by a primary urging member to come into contact with the intermediate transfer belt at portions that become a plurality of primary transfer positions on an inner circumferential surface of the intermediate transfer belt, The intermediate transfer unit is an image forming apparatus described in any one of ((1)) to (((3))), wherein a primary transfer roll of a portion of the plurality of primary transfer rolls is maintained in a state spaced apart from the intermediate transfer belt when the movable body is moved by the cam. (((5))) the intermediate transfer unit includes a second cam that is fixed to a second cam shaft disposed on the support and that holds the remaining primary transfer rolls other than the part of the primary transfer rolls in a state in which the remaining primary transfer rolls are moved to the inside of the intermediate transfer belt, and a lever that is fixed to the second cam shaft and is operated to move the second cam, The lever is operated to keep the remaining primary transfer roll in a state moved to the inside of the intermediate transfer belt by the second cam when the intermediate transfer unit is being attached or detached (((4))).

[0207] According to the image forming apparatus of (((1))), it is easier to engage the cam side shaft coupling and the drive side shaft coupling when the detachable unit is attached, compared to a case in which a biasing member that biases the cam shaft in a rotatable direction when it is not connected to the drive transmission shaft is provided on the detachable unit side. According to the image forming apparatus of (((2))), the cam side shaft coupling and the drive side shaft coupling are more likely to engage with each other even if the cam of the detachable unit moves the movable body to become immobile, compared to when the biasing member is configured to bias the cam side shaft coupling so that the range of motion of the cam side shaft coupling is wider than the range of motion of the drive side shaft coupling. According to the image forming apparatus of (((3))), the urging member can be easily made to function even when the drive transmission shaft rotates in the forward and reverse directions, compared to when the urging member is a urging member other than a tension spring. According to the image forming device of (((4))), it is easier to engage the cam side shaft coupling and the drive side shaft coupling when the intermediate transfer unit is attached, compared to a case in which a biasing member that biases the cam shaft in a rotatable direction when it is not connected to the drive transmission shaft is provided on the intermediate transfer unit side. According to the image forming device of (((5))), compared to a case in which a biasing member that biases the cam shaft in a rotatable direction when it is not connected to the drive transmission shaft is provided on the removable unit side, it is possible to eliminate the need to operate a lever to release the immobilized state caused by the cam of the intermediate transfer unit moving the movable body. [Explanation of symbols]

[0208] 1. Image forming device 10…Housing (an example of the main body) 25Y, 25M, 25C, 25K...primary transfer roll (an example of multiple primary transfer rolls) 30...Intermediate transfer unit (an example of a detachable unit) 31...Intermediate transfer belt 32, 33, 34, 35...Belt support rolls (an example of multiple rotating rolls) 50F, 50R…Support frame (an example of a support) 51F, 51R...moving frame (an example of a moving body) 52F, 52R...First cam (example of cam) 53...First camshaft (an example of a camshaft) 54…Cam side shaft coupling 55…Fitting part 59y, 59m, 59c, 59k...Compression coil spring (an example of a primary biasing member) 71...Drive transmission shaft 72... Passive gear 73...Drive side shaft coupling 74…Fitting part 76...Mobile transmission body 78... Urging member (e.g., tension coil spring) 75...Moving link with rack gear (an example of a moving transmission mechanism) 95…Lever 520…Second Cam 561…Second camshaft D1, D2: Direction in which the moving object moves

Claims

1. A main body having an image forming unit; A detachable unit having a support body that is detachably attached to the main body; A movable body that is movably disposed relative to the support and is biased in one direction; a cam that moves the moving body in a direction opposite to the one direction; a cam shaft rotatably disposed on the support and having the cam fixed thereto; a cam-side shaft coupling attached to one end of the camshaft and having a fitting portion; a drive transmission shaft rotatably disposed on the main body side and having a passive gear fixed thereto for receiving the power transmission; a drive-side shaft coupling attached to one end of the drive transmission shaft and having a fitted portion into which the fitting portion is fitted; a moving transmission body that is disposed on the main body side and meshes with the passive gear to move within a certain range to transmit power; a biasing member that is disposed on the main body side and biases the drive transmission shaft in a rotatable direction when the fitting portion and the fitted portion are not fitted to each other; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the biasing member biases the drive-side shaft coupling so that a movable range of the drive-side shaft coupling is wider than a movable range of the cam-side shaft coupling when the engaging portion and the engaged portion are not engaged with each other.

3. 3. The image forming apparatus according to claim 2, wherein the biasing member is a tension spring having one end attached to a portion of the main body and the other end attached to an eccentric portion of the other end of the drive transmission shaft.

4. the removable unit is an intermediate transfer unit having an intermediate transfer belt that is rotated around a plurality of rotating rolls that are arranged on the support, and a plurality of primary transfer rolls that are arranged on the support and are urged by a primary urging member to come into contact with the intermediate transfer belt at portions that become a plurality of primary transfer positions on an inner circumferential surface of the intermediate transfer belt, 2 . The image forming apparatus according to claim 1 , wherein the intermediate transfer unit is configured such that a portion of the plurality of primary transfer rolls is held in a state spaced apart from the intermediate transfer belt when the movable body is moved by the cam.

5. the intermediate transfer unit includes a second cam that is fixed to a second cam shaft disposed on the support and that holds the remaining primary transfer rolls other than the part of the primary transfer rolls in a state in which the remaining primary transfer rolls are moved to the inside of the intermediate transfer belt, and a lever that is fixed to the second cam shaft and is operated to move the second cam, 5. The image forming apparatus according to claim 4, wherein the lever is operated to keep the remaining primary transfer roll in a state where it is moved to the inside of the intermediate transfer belt by the second cam when the intermediate transfer unit is being installed or removed.

Images