JP2016071156A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device 1 capable of realizing control of states of separations among transfer rollers for various different colors at low cost.SOLUTION: An image formation device includes: a frame moving part 402 moving a frame 500; a position detecting part 303 detecting the position of the frame 500; and a separation controlling part 304 controlling separation and contact of a transfer roller with respect to an intermediate transfer belt. The separation controlling part 304 moves the frame 500 and positions the frame 500 in one of first, second, and third locations based output of the position detecting part 303, the first location being where a plurality of transfer rollers are all in contact with the intermediate transfer belt, the second location being where the plurality of transfer rollers are all separated from the intermediate transfer belt, and the third location being where a specific one of the transfer rollers is in contact with intermediate transfer belt.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus capable of realizing control of a separation state of a photosensitive drum for each color at a low cost.

  In recent years, image forming apparatuses capable of performing monochrome printing and color printing have become widespread. In such image forming apparatuses, only black (K) photosensitive drums are brought into contact with the intermediate transfer belt during monochrome printing, and color printing is performed. At the time of printing, four types of photosensitive drums in which yellow (Y), magenta (M), and cyan (C) are added to black (K) are switched so as to contact the intermediate transfer belt. By such switching, wear of the photosensitive drum brought into contact with the intermediate transfer belt is prevented.

  As a technique related to such a switching function, for example, Japanese Patent Laid-Open No. 2011-253082 (Patent Document 1) discloses a common position setting in which each developer carrier and each image carrier are set to be variable by linear movement. An image forming apparatus having a drive device for linearly moving the member and the position setting member is disclosed. As a result, space saving is achieved with a simple structure.

  JP-A-10-339976 (Patent Document 2), JP-A-2007-79570 (Patent Document 3), and JP-A-2007-79571 (Patent Document 4) use a plurality of sensors. Controls switching between monochrome printing and color printing.

  Japanese Patent Application Laid-Open No. 2007-17508 (Patent Document 5) uses a transfer current amount even when the contact state of the transfer conveyance belt is unknown when performing a residual transfer material detection operation. An image forming apparatus that correctly detects a residual transfer material by executing an operation for changing the state of the transfer conveyance belt is disclosed.

JP 2011-253082 A JP 10-339976 A JP 2007-79570 A JP 2007-79571 A JP 2007-17508 A

  However, since the technique described in Patent Document 1 described above uses a stepping motor, there is a problem that the cost is increased. Further, in the technique described in Patent Documents 2-4, the number of sensors increases, so that there is a problem of cost increase. Further, in the technique described in Patent Document 5, since the transfer current amount is used, erroneous detection is likely to occur due to environmental conditions, and there is a problem that detection processing is complicated as compared with the case where an actuator is used. In addition, there is a problem that the detection processing circuit is expensive.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of controlling the separation state of the photosensitive drum for each color at a low cost. To do.

  In order to solve the above-described problems and achieve the object, an image forming apparatus according to the present invention includes an intermediate transfer belt, a plurality of image carriers arranged in series in the rotation direction of the intermediate transfer belt, and the intermediate transfer belt. A tandem full-color image forming apparatus including a plurality of transfer rollers arranged to face the plurality of image carriers with a transfer belt interposed therebetween, and adopts the following configuration.

  The image forming apparatus according to the present invention includes a switching mechanism that switches the separation and contact of the transfer roller with respect to the intermediate belt, and the switching mechanism extends in the arrangement direction of the image carrier and is movable in the arrangement direction. A pair of frames that support both ends of the shafts of the plurality of transfer rollers and switch the separation and contact of the transfer rollers, a frame moving unit that moves the frame, a position detection unit that detects the position of the frame, and the transfer A separation control unit that controls separation and contact of the roller with respect to the intermediate transfer belt. The separation control unit moves the frame and, based on the output of the position detection unit, a first position for bringing all of the plurality of transfer rollers into contact with the intermediate transfer belt, and all of the plurality of transfer rollers. At a second position where the frame is separated from the intermediate transfer belt and a third position where only a predetermined transfer roller of the plurality of transfer rollers is brought into contact with the intermediate transfer belt. Position.

  In addition, the first pattern of the output of the position detection unit showing the case where the state is shifted from the first state to the third state, and the transmitted light which shows the case where the state is shifted from the first state to the second state. A second pattern of the detection signal, the separation control unit collates the first pattern or the second pattern with the output of the position detection unit, from the first state, Switch to the second state or the third state.

  The apparatus further includes a guide unit that controls the transfer roller to and from the intermediate belt for each transfer roller by guiding a small roller that supports the transfer roller according to the movement of the frame.

  According to the image forming apparatus of the present invention, it is possible to control the separation state of the photosensitive drum for each color at a low cost.

1 is a conceptual diagram showing an overall internal configuration of an image forming apparatus according to the present invention. FIG. 3 is a diagram illustrating a configuration of control system hardware of an image forming apparatus according to the present invention. It is a functional block diagram of the present invention. It is a flowchart for showing the execution procedure of this invention. FIG. 5 is a diagram (FIG. 5A) illustrating an example of a separation / contact relationship between a frame and a primary transfer roller according to the present invention, and a diagram (FIG. 5B) illustrating an example of a frame moving mechanism according to the present invention. FIG. 6A shows an example of a four-color pressing state according to the present invention (FIG. 6A), FIG. 6B shows an example of a three-color release state according to the present invention, and FIG. FIG. 6C shows an example of the pattern (FIG. 6C). FIG. 7A shows an example of a four-color pressing state according to the present invention (FIG. 7A), FIG. 7B shows an example of a four-color release state according to the present invention, and FIG. It is a figure (FIG.7 (C)) which shows an example of this pattern. It is a figure (Drawing 8 (A)) which shows an example of the 3rd pattern concerning the present invention, and a figure (Drawing 8 (B)) which shows an example of the 4th pattern concerning the present invention.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. In addition, the following embodiment is an example which actualized this invention, Comprising: The thing of the character which limits the technical scope of this invention is not. Moreover, the alphabet S added before the number in a flowchart means a step.

  The image forming apparatus 1 according to the present invention will be described below. The image forming apparatus 1 transfers a toner image formed by the tandem-type image forming unit A1 that forms a toner image based on image data, a paper storage unit 2 that stores paper, and the image forming unit A1 onto the paper. A next transfer unit 3 is provided. Further, a fixing unit 4 for fixing the transferred toner image on the paper, a paper discharge device 5 for discharging the paper on which the fixing has been completed, and a paper discharge tray 7 for receiving the discharged paper are provided. Further, the image forming apparatus 1 includes a paper transport unit 6 that transports paper from the paper storage unit 2 to the paper discharge device 5.

  The image forming unit A1 includes an intermediate transfer belt B1 (intermediate transfer member), a cleaning unit B2 for cleaning the intermediate transfer belt B1, and colors of yellow (Y), magenta (M), cyan (C), and black (K). Are provided with image forming units FY, FM, FC, and FB, respectively.

  The intermediate transfer belt B1 is an endless belt-like member that is wider than the maximum length sheet in the direction perpendicular to the usable sheet conveyance direction and has a conductive shape. Is done.

  The image forming units FY, FM, FC, and FK are arranged in this order along the intermediate transfer belt B1 in the moving direction of the intermediate transfer belt B1, downstream of the cleaning unit B2 and upstream of the secondary transfer unit 3. .

  Under such a configuration, the image forming apparatus 1 that has received an instruction for image formation from a host device such as a personal computer (PC) or the like forms toner images of each color corresponding to the received image data in the image forming units FY, FM. , FC, and FB. In the case of color printing, the image forming apparatus 1 transfers the toner images of all colors to the intermediate transfer belt B1, and superimposes them on this to form a color toner image. In the case of monochrome printing, the image forming apparatus 1 transfers a black (K) color toner image to the intermediate transfer belt B1 to form a monochrome toner image.

  In synchronism with the formation of the toner image, the sheets stored in the sheet storage unit 2 are taken out from the sheet storage unit 2 one by one and conveyed on the sheet conveyance unit 6. Then, the sheet is fed to the secondary transfer unit 3 in synchronization with the primary transfer to the intermediate transfer belt B1, and the toner image on the intermediate transfer belt B1 is secondarily transferred to the sheet by the secondary transfer unit 3. The sheet on which the toner image has been transferred is conveyed to the fixing unit 4, and the color toner image is fixed to the sheet by heat and pressure. The sheet is discharged from the discharge tray unit provided on the outer periphery of the image forming apparatus 1. 7 is discharged. The toner remaining on the intermediate transfer belt B1 after the secondary transfer is removed from the intermediate transfer belt B1 by the cleaning unit B2.

  As shown in FIG. 2, the image forming apparatus 1 corresponds to a CPU (Central Processing Unit) 201, a RAM (Random Access Memory) 202, a ROM (Read Only Memory) 203, an HDD (Hard Disk Drive) 204, and each drive unit. A driver 205 is connected via an internal bus 206.

  The CPU 201 uses, for example, the RAM 202 as a work area, executes a program stored in the ROM 203, the HDD 204, etc., and exchanges data and commands with the driver 205 based on the execution result, as shown in FIG. The operation of each driving unit is controlled. Also, each unit (shown in FIG. 3) described later other than the drive unit operates as each unit when the CPU 201 executes a program.

  Next, the configuration and execution procedure according to the embodiment of the present invention will be described with reference to FIGS. 3 and 4.

  First, when a user transmits an image formation instruction (print job) including image data and printing conditions (for example, monochrome printing, color printing, etc.) from the host apparatus to the image forming apparatus 1, image formation of the image forming apparatus 1 is performed. The unit 301 receives the print job (FIG. 4: S101), and the frame moving unit 302 displays a frame for switching the (primary) transfer roller for each color with respect to the intermediate transfer belt B1 on the surface of the intermediate transfer belt B1. It moves according to the direction (FIG. 4: S102).

  Here, the method of moving the frame moving unit 302 is not particularly limited. For example, as shown in FIG. 5A, first, in a front view, a pair of long frames 500 extend in the arrangement direction of the photosensitive drums AY, AM, AC, AB for each color, and in the arrangement direction. It is movable and is arranged with its longitudinal direction corresponding to the surface direction of the intermediate transfer belt B. Below the intermediate transfer belt B, there are provided photosensitive drums AY, AM, AC, AB in image forming unit units FY, FM, FC, FB for each color, and photosensitive drums AY, AM, AC, AB for each color. AB is in contact with the intermediate transfer belt B1. Above the intermediate transfer belt B1, primary transfer rollers RK, RC, RM, RY for each color are provided facing the photosensitive drums AY, AM, AC, AB, and the primary transfer rollers RK, RC. , RM and RY are always pressed by an urging means (spring or the like) not shown so as to contact the intermediate transfer belt B1.

  On the other hand, a support mechanism for supporting the primary transfer rollers RK, RC, RM, and RY for each color so as to be movable in the vertical direction is provided, and one end of each support mechanism is provided at both ends of the shafts of the small rollers BK, BC, BM, and BY. The arm part 500a which connects and connects the other end to the both ends of the axial part of primary transfer roller RK, RC, RM, RY is provided. Both end portions of the arm portion 500a constitute a bearing that rotatably supports each shaft portion.

  Here, a switching mechanism is provided on a side surface portion of the frame 500, and the small rollers BK, BC, BM, BY are mounted, and a guide portion CK that guides the small rollers BK, BC, BM, BY in the vertical direction. , CC, CM, CY has a horizontal reference surface and a moving surface, and an inclined surface connecting the reference surface and the moving surface, along which the small rollers BK, BC, BM, BY move relatively up and down. To do. The shape of the guide portions CK, CC, CM, and CY for each color is the same as that of the guide portions CC, CM, and CY for cyan, magenta, and yellow, and only the shape of the guide portion CK for black color is used. Unlike the shapes of the guide portions CC, CM, and CY, the height of the moving surface of the black color guide portion CK is lower than the moving surfaces of the other guide portions CC, CM, and CY. Then, when the frame 500 moves in the rotation direction or the reverse rotation direction of the intermediate transfer belt B1, the small rollers BK, BC, BM, BY are guided by the guide portions CK, CC, CM, CY and moved in the vertical direction. Is done.

  The small rollers BK, BC, BM, BY are moved upward (in a direction away from the intermediate transfer belt B1), so that the primary transfer rollers RK, RC, RM, RY are lifted upward from the intermediate transfer belt B1. Separate. On the other hand, the primary rollers RK, RC, RM, RY are pressed downward (by the urging means) by moving the small rollers BK, BC, BM, BY downward (in the direction contacting the intermediate transfer belt B1). Then, it comes into contact with the intermediate transfer belt B1.

  By appropriately changing the configuration of the guide portions CK, CC, CM, and CY, for example, the state in which the primary transfer rollers RK, RC, RM, and RY of all colors are in contact with the intermediate transfer belt B1 (four-color pressing state) ), A state in which only the primary transfer roller RK of black (K) is brought into contact with the intermediate transfer belt B1 (a state in which the three colors are released), and the primary transfer rollers RK, RC, RM, and RY of all colors are connected to the intermediate transfer belt B1. It is possible to switch the state separated from (4 color release state) by moving the frame 500.

  Further, as shown in FIG. 5B, a rack gear portion 501 is provided in advance along a longitudinal direction at a predetermined portion below the frame 500, and meshes with the rack gear portion 501 to A rotation gear portion 502 (pinion) that is rotatably supported and moves the frame 500 is further provided. The frame moving unit 302 uses a predetermined motor (for example, a brushless motor) to rotate the rotating gear unit 502 in a predetermined direction (for example, a clockwise direction or a counterclockwise direction), thereby the rack gear unit 501. The frame 500 can be moved in the rotation direction or the reverse rotation direction of the intermediate transfer belt B1 through the above.

  When the image forming unit 301 starts to move the frame 500 of the frame moving unit 302, the position detecting unit 303 includes a light shielding plate 504 having a plurality of openings provided along the longitudinal direction of the frame, Based on a light-emitting unit 506 and a light-receiving unit 507 (sensor) that are provided with the light-shielding plate 504 interposed therebetween and are immovable with respect to the image forming apparatus 1, transmitted light transmitted from the opening 505 of the light-shielding plate 504 is detected (FIG. 4: S103).

  Here, the method detected by the position detection unit 303 is not particularly limited. For example, as illustrated in FIG. 5A, a rectangular light shielding plate 504 is provided in advance along a longitudinal direction of the frame 500 in a part of a side surface portion of the frame 500 in a plan view. The light shielding plate 504 is provided with a plurality of (here, five) openings 505 (slits) of a predetermined size in series along the longitudinal direction of the frame 500. On the other hand, a light emitting unit 506 and a light receiving unit 507 are provided so as to sandwich the light shielding plate 504. The light emitting unit 506 and the light receiving unit 507 are, for example, inexpensive photo interrupters. The light emitting unit 506 and the light receiving unit 507 are fixed to the main body frame 500, and only the frame 500 moves in parallel to the surface direction of the intermediate transfer belt B1.

  When the position detection unit 303 irradiates light from the light emitting unit 506 toward the light shielding plate 504, the light receiving unit 507 does not receive transmitted light unless the light shielding plate 504 facing the light emitting unit 506 has the opening 505. On the other hand, if the light shielding plate 504 facing the light emitting unit 506 has the opening 505, the light from the light emitting unit 506 passes through the opening 505 and is irradiated to the light receiving unit 507. As described above, the position detection unit 303 may or may not detect transmitted light according to the position of the light shielding plate 504 with respect to the light emitting unit 506 and the light receiving unit 507.

  When the image forming unit 301 starts detecting the transmitted light of the position detecting unit 303, the separation control unit 304 moves the frame 500 based on the transmitted light detection signal (FIG. 4: S104). Then, the print job is stopped at a position corresponding to the print job (instruction) (FIG. 4: S105).

  Here, the method by which the separation control unit 304 stops the movement of the frame 500 is not particularly limited. For example, when the current state is the four-color pressing state corresponding to color printing, and the print job instruction corresponds to monochrome printing and the state is shifted to the three-color canceling state, the following occurs.

  When the frame moving unit 302 rotates the rotating gear unit 502 in the counterclockwise direction and the frame 500 is translated in the direction opposite to the rotating direction of the intermediate transfer belt B1, as shown in FIG. FIG. 6B shows a state in which the primary transfer rollers RK, RC, RM, and RY of all colors are in contact with the intermediate transfer belt B1 (four-color pressing state) by the configuration of the portions CK, CC, CM, and CY. As shown, cyan (C), magenta (M), and yellow (Y) primary transfer rollers RC, RM, and RY other than black (K) are separated from the intermediate transfer belt B1 (three colors). (Release state).

  Further, due to the presence of the opening 505 of the light shielding plate 504 of the frame 500, the position detection unit 303 moves from the state where it has not detected the transmitted light until now to FIG. 6B. In the process, transmitted light is detected or not detected.

  Here, as shown in FIG. 6C, a first pattern of transmitted light detection signals (HI signal, LOW signal) corresponding to the position of the frame 500 from the four-color pressed state to the three-color released state. (A pattern for shifting from the four-color pressed state to the three-color released state) is stored in a predetermined memory in advance. A home position pattern indicating the home position of the frame 500 is also stored in the memory. The separation controller 304 detects the home position of the frame 500 by comparing the transmitted light detection signal detected corresponding to the movement of the frame 500 and the home position pattern, and the frame from this position The transmitted light detection signal detected corresponding to the movement of 500 is compared with the first pattern, and the detected transmitted light detection signal matches the first pattern (see FIG. 4: S104), the separation controller 304 stops the movement of the frame 500 (FIG. 4: S105).

  Here, it is shown that the first pattern becomes the HI signal only three times from the LOW signal. Therefore, when the separation control unit 304 continuously counts the HI signal from the LOW signal three times (time t1), it is determined that the detected signal of the transmitted light matches the first pattern. Then, the movement of the frame 500 is stopped (FIG. 4: S105). As a result, the frame 500 can be appropriately stopped at a position corresponding to the three-color release state only with a transmitted light detection signal (HI signal, LOW signal). In other words, by storing a plurality of patterns in the memory, a plurality of positionings can be performed by one sensor (light emitting unit 506 and light receiving unit 507). Therefore, a plurality of sensors are not necessary.

  When the separation control unit 304 stops the frame 500, the image forming unit 301 executes image formation based on the print job (FIG. 4: S106). In the case described above, image formation is executed by monochrome printing after shifting from the four-color pressed state corresponding to color printing to the three-color release state corresponding to monochrome printing.

  By the way, in S104, the current state is the four-color pressed state. For example, the instruction cancels four colors corresponding to replacement of each part (primary transfer roller, photosensitive drum, etc.) of the image forming unit or removal of each part. When shifting to a state, it is as follows.

  First, as shown in FIG. 7A, when the four-color pressed state frame 500 continues to translate in the direction opposite to the rotation direction of the intermediate transfer belt B1, the four-color pressed state goes through the three-color released state, As shown in FIG. 7B, the primary transfer rollers RK, RC, RM, and RY of all colors are shifted to a state where they are separated from the intermediate transfer belt B1 (four-color release state).

  Here, as shown in FIG. 7C, the second pattern of the detection signal of the transmitted light (from the four-color pressed state to the four-color pressed state corresponding to the positions from the four-color pressed state to the four-color released state of the frame 500. The pattern for shifting to the color release state) is stored in a predetermined memory in advance. This second pattern indicates that the HI signal has been changed six times from the LOW signal, and a predetermined time (Δt) has elapsed since the last HI signal was detected. For this reason, the separation control unit 304 continuously counts the HI signal from the LOW signal six times, and when a predetermined time (Δt) has elapsed since the last HI signal was counted (time t2) (FIG. 4). : S104), the movement of the frame 500 is stopped (FIG. 4: S105). As a result, the frame 500 can be appropriately stopped from the four-color pressed state to a position corresponding to the three-color release state and the four-color release state only by the transmitted light detection signal (HI signal, LOW signal). .

  Furthermore, in S104, when the current state is the three-color release state and the state is shifted to the four-color pressing state, for example, the frame 500 is moved rightward from the state of FIG. 6B, and FIG. When shifting to this state, it is as follows.

  First, when the frame moving unit 302 rotates the rotating gear unit 502 in the clockwise direction and the frame 500 is translated in the rotational direction of the intermediate transfer belt B1, the state shifts from the three-color release state to the four-color pressing state.

  Here, as shown in FIG. 8A, the third pattern of the transmitted light detection signal (from the three-color release state to the four-color release state) corresponding to the position from the three-color release state to the four-color pressed state of the frame 500. A pattern for shifting to the color pressing state) is stored in a predetermined memory in advance. This third pattern shows that it becomes a LOW signal only three times from the HI signal. When the separation control unit 304 continuously counts the LOW signal from the HI signal three times (time t3) (FIG. 4: S104), the movement of the frame 500 is stopped (FIG. 4: S105). This is exactly the reverse of the operation of FIG.

  In S104, when the current state is the four-color release state and the state is shifted to the four-color pressing state, for example, the frame 500 is moved rightward from the state shown in FIG. When shifting to this state, it is as follows.

  First, when the frame moving unit 302 rotates the rotating gear unit 502 in the clockwise direction and the frame 500 is translated in the rotational direction of the intermediate transfer belt B1, the four-color released state passes through the three-color released state, and then the 4 Transition to the color pressing state.

  Here, as shown in FIG. 8B, the fourth pattern of the transmitted light detection signal (from the four-color release state to the four-color release state) corresponds to the position of the frame 500 from the four-color release state to the four-color press state. A pattern for shifting to the color pressing state) is stored in a predetermined memory in advance. This fourth pattern indicates that a LOW signal has been changed six times from the HI signal, and a predetermined time (Δt) has elapsed since the last LOW signal was detected. Therefore, the switching unit 304 continuously counts the LOW signal from the HI signal six times, and when a predetermined time (Δt) has elapsed from the time when the last LOW signal was counted (time t4) (FIG. 4: S104), the movement of the frame 500 is stopped (FIG. 4: S105). This is exactly the reverse of the operation of FIG.

  In this way, a pattern of a detection signal of transmitted light corresponding to a predetermined position of the frame 500 is prepared in advance, and the switching unit 304 is a pattern corresponding to a predetermined instruction (color printing, monochrome printing, replacement of each part, maintenance, etc.). Is used to control the movement of the frame 500. Thereby, it is possible to identify a plurality of states based on the detection signal of the transmitted light from one sensor and shift to a state corresponding to the instruction.

  In the embodiment of the present invention, the openings 505 having predetermined dimensions are alternately arranged at predetermined intervals on the light-shielding plate 504, so that each state can be determined in accordance with the count of the HI signal or the LOW signal of the transmitted light detection signal. However, other configurations may be used. For example, when shifting from the transition source state to the transition destination state, the size and interval of the opening 505 may be changed as appropriate according to the characteristics of each state.

  In the embodiment of the present invention, it is assumed that the primary transfer roller is separated from the intermediate transfer belt B1, but there is no particular limitation, and the present invention is applied to the predetermined roller (photosensitive drum or the like) separated from the predetermined belt B1. It doesn't matter.

  In the embodiment of the present invention, the identification of the three states of the four-color pressed state, the three-color released state, and the four-color released state is assumed, but other configurations may be used. In other words, the number of states that can be identified can be increased according to the number, size, and the like of the openings 505 of the light shielding plate 504, and thus it is not necessary to limit the identification to three states.

  As described above, the image forming apparatus according to the present invention is useful not only for a color / monochrome compound machine but also for a color / monochrome copying machine, a color / monochrome printer, etc., and controls the separation state of the photosensitive drum for each color. It is effective as an image forming apparatus that can be realized at low cost.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 301 Image forming part 302 Frame moving part 303 Position detection part 304 Separation control part

Claims (3)

An intermediate transfer belt, a plurality of image carriers arranged in series in the rotation direction of the intermediate transfer belt, and a plurality of transfer rollers arranged to face the plurality of image carriers with the intermediate transfer belt interposed therebetween. In the tandem full-color image forming apparatus provided,
A switching mechanism for switching the contact and separation of the transfer roller with respect to the intermediate belt;
The switching mechanism is
A pair of frames that extend in the arrangement direction of the image carriers, are movable in the arrangement direction, support both ends of the shaft portions of the plurality of transfer rollers, and switch the separation and contact of the transfer rollers;
A frame moving unit for moving the frame;
A position detector for detecting the position of the frame;
A separation control unit for controlling separation and contact of the transfer roller with respect to the intermediate transfer belt,
The separation control unit moves the frame and, based on the output of the position detection unit, a first position for bringing all of the plurality of transfer rollers into contact with the intermediate transfer belt, and all of the plurality of transfer rollers. At a second position where the frame is separated from the intermediate transfer belt and a third position where only a predetermined transfer roller of the plurality of transfer rollers is brought into contact with the intermediate transfer belt. An image forming apparatus characterized by positioning. The first pattern of the output of the position detection unit showing the case where the state has shifted from the first state to the third state, and the detection of transmitted light which shows the case where the state has shifted from the first state to the second state A second pattern of signals,
The separation control unit collates the first pattern or the second pattern with the output of the position detection unit, and switches from the first state to the second state or the third state. Item 2. The image forming apparatus according to Item 1. The guide unit according to claim 1, further comprising: a guide unit configured to control a separation roller of the transfer roller with respect to the intermediate belt for each transfer roller by guiding a small roller that supports the transfer roller according to the movement of the frame. The image forming apparatus described in 1.