Image forming apparatus

Abstract

To provide an image forming apparatus that can determine a state of pressure-contact / separation of an intermediate transfer belt with / from an image carrier without toner consumption.SOLUTION: An image forming apparatus 10 has: a process unit Pa that has a photoreceptor drum 30a, and forms a toner image on the photoreceptor drum 30a; an intermediate transfer belt 21 to a surface of which the toner image on the photoreceptor drum 30a is intermediately transferred; an intermediate transfer roller 24a whose position can be changed by manual operations to a first position where it brings the surface of the intermediate transfer belt 21 into contact with the photoreceptor drum 30a, and a second position where it separates the intermediate transfer belt 21 from the photoreceptor drum 30a; an image density sensor 40 that detects the toner image on the intermediate transfer belt 21, and whose relative position to the intermediate transfer belt 21 changes according to whether the intermediate transfer roller 24a is at the first position or the second position; and a control unit 60 that determines whether the intermediate transfer roller 24a is at the first position or the second position on the basis of a detection value from the image density sensor 40.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an intermediate transfer type image forming apparatus. [Background technology]

[0002] There are known intermediate transfer type image forming devices in which a toner image formed on a photosensitive member is intermediately transferred (primary transfer) to an intermediate transfer belt, and the toner image intermediately transferred to the intermediate transfer belt is then transferred (secondary transfer) to recording paper. Some intermediate transfer type image forming devices allow the intermediate transfer belt to be manually switched between pressed and separated from the photosensitive member. The intermediate transfer belt is pressed against and separated from the photosensitive member by manually changing the position of the intermediate transfer roller, but if the intermediate transfer belt is not returned to the pressed state when an image formation operation is performed, the toner image formed on the photosensitive member will not be transferred, and toner will be wasted.

[0003] Patent Document 1 discloses that an image density sensor is used to determine whether a transfer (secondary transfer) roller is in pressure contact or separation. In the determination method of Patent Document 1, if the toner density on the intermediate transfer belt after the toner image intermediately transferred onto the intermediate transfer belt passes through the transfer (secondary transfer) roller is low, the transfer (secondary transfer) roller is determined to be in a pressure contact state, and if the toner density on the intermediate transfer belt is high, the transfer (secondary transfer) roller is determined to be in a separation state. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-17995 Summary of the Invention [Problem to be solved by the invention]

[0005] The determination method of Patent Document 1 requires an intermediate (primary) transfer operation of the toner image from the photosensitive member to the intermediate transfer belt, and toner consumption occurs during the determination.

[0006] The present disclosure has been made in view of the above-mentioned problems, and aims to provide an image forming apparatus that can determine the state of an intermediate transfer roller pressed against / separated from an image carrier without consuming toner. [Means for solving the problem]

[0007] In order to solve the above problems, the image forming apparatus of the present disclosure is characterized by having an image forming unit having an image carrier and forming a toner image on the image carrier; an intermediate transfer belt stretched by multiple rollers onto whose surface the toner image on the image carrier is intermediately transferred; an intermediate transfer roller, which is one of the multiple rollers, and whose position can be changed manually between a first position where the surface of the intermediate transfer belt is brought into contact with the image carrier, and a second position where the intermediate transfer belt is separated from the image carrier; an image density sensor, which is a sensor that detects the toner image on the intermediate transfer belt, and whose relative position with respect to the intermediate transfer belt changes when the intermediate transfer roller is in the first position or the second position; and a control unit that determines whether the intermediate transfer roller is in the first position or the second position based on the detection value of the image density sensor.

[0008] According to the above configuration, the intermediate transfer roller can be determined to be in pressure contact / separation state based on the change in the relative position between the intermediate transfer belt and the image density sensor, eliminating the need to form a toner image for the determination and eliminating unnecessary toner consumption.

[0009] Furthermore, in the image forming apparatus, the control unit may be configured not to permit the image forming unit to form a toner image when it is determined that the intermediate transfer roller is at the second position.

[0010] According to the above configuration, when it is determined that the intermediate transfer roller is in the second position (separated state), the formation of a toner image is not permitted, so that image formation that would result in unnecessary toner consumption can be effectively prevented.

[0011] The image forming device may also include a drive roller, which is one of the plurality of rollers, that moves and rotates the intermediate transfer belt in a predetermined movement direction, and a transfer member that contacts the surface of the intermediate transfer belt on the drive roller and is arranged to rotate together with the intermediate transfer belt, and that transfers the toner image intermediately transferred onto the intermediate transfer belt to the sheet by clamping and transporting the sheet at a nip portion, which is the contact area with the intermediate transfer belt, and the image density sensor may be configured to be located downstream of the intermediate transfer roller and upstream of the nip portion in the movement direction of the intermediate transfer belt.

[0012] According to the above configuration, the image density sensor can be disposed at a position where its relative position to the intermediate transfer belt changes significantly depending on whether the intermediate transfer roller is pressed against or separated from the intermediate transfer belt.

[0013] The image forming device can also be configured to include an opposing roller, one of the plurality of rollers, that moves the intermediate transfer belt to a position where the distance between the surface of the intermediate transfer belt and the image density sensor is a predetermined distance when the intermediate transfer roller is in the first position, and moves the intermediate transfer belt to a position where the distance between the surface of the intermediate transfer belt and the image density sensor is greater than the predetermined distance when the intermediate transfer roller is in the second position, in a position opposite the image density sensor.

[0014] According to the above configuration, by providing an opposing roller at a position opposite the image density sensor, the distance between the intermediate transfer belt and the image density sensor can be changed with high precision according to the pressure contact / separation of the intermediate transfer roller.

[0015] In the image forming apparatus, the image density sensor includes a light-emitting unit that emits light toward the intermediate transfer belt and a light-receiving unit that receives light reflected from the intermediate transfer belt and outputs an output signal according to the amount of light received, and when determining whether the intermediate transfer roller is at the first position or the second position, the control unit causes the light-emitting unit to emit light, and determines that the intermediate transfer roller is at the first position if the value of the output signal from the light-receiving unit, which is the detection value detected by the image density sensor, is within a predetermined determination range, and determines that the intermediate transfer roller is at the second position if the value of the output signal from the light-receiving unit is not within the determination range. It can be configured as follows.

[0016] The image forming apparatus may further include a display unit, and the control unit may be configured to display on the display unit that the intermediate transfer belt is separated from the image carrier when the intermediate transfer roller is in the second position.

[0017] In the image forming apparatus, the image forming unit includes a charging roller that is supplied with a charging bias having a predetermined voltage value and charges the image carrier to a predetermined potential, an exposure device that exposes the image carrier charged to the predetermined potential to form an electrostatic latent image, and a developing device that contains toner and develops the electrostatic latent image with the toner when a developing bias having a predetermined voltage value is supplied, and the control unit supplies the charging bias to the charging roller and the developing bias to the developing device after it is determined that the intermediate transfer roller is at the first position. However, a confirmation operation including an image forming operation for forming a toner image on the image carrier and an intermediate transfer operation to the intermediate transfer belt is performed without exposing the image carrier to light by the exposure device, and if the image density sensor does not detect a toner image within a specified time during which the confirmation operation is performed, it is determined that the charging roller is in contact with the image carrier, and if the image density sensor detects a toner image within the specified time, it is determined that the charging roller is in an abnormal state where it is not in contact with the image carrier. [Effects of the Invention]

[0018] The image forming apparatus of the present disclosure determines whether the intermediate transfer roller is pressed against or separated from the image carrier based on changes in the relative position between the intermediate transfer belt and the image density sensor, thereby achieving the effect of being able to determine the state of the intermediate transfer roller being pressed against or separated from the image carrier without consuming toner. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic diagram illustrating a basic configuration of an image forming apparatus according to the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing the structure of the periphery of the intermediate transfer unit when it is attached to the main body (when forming a color image). [Figure 3] FIG. 4 is a schematic diagram illustrating the structure around the intermediate transfer unit in a state where it is being removed; [Figure 4] FIG. 2 is a schematic diagram showing the structure of the periphery of the intermediate transfer unit when it is attached to the main body (during monochrome image formation and standby). [Figure 5] FIG. 2 is a schematic diagram illustrating the structure of the periphery of the intermediate transfer unit in a state where the intermediate transfer roller is spaced apart from the photosensitive drum. [Figure 6] 10 is a schematic diagram showing an example of a switching mechanism for manually changing the positions of the intermediate transfer roller and the counter roller, showing the intermediate transfer roller in a pressure contact state. FIG. [Figure 7] 10 is a schematic diagram showing an example of a switching mechanism for manually changing the positions of the intermediate transfer roller and the counter roller, showing the state in which the intermediate transfer roller is in a separated state. FIG. [Figure 8A] 10 is a side view of the intermediate transfer belt and the image density sensor as viewed from the drive roller side, showing the pressure contact state of the intermediate transfer roller. FIG. [Figure 8B] 10 is a side view of the intermediate transfer belt and the image density sensor as viewed from the drive roller side, showing the intermediate transfer roller in a separated state. FIG. [Figure 9] 10 is a flowchart illustrating an example of pressure contact / separation determination of an intermediate transfer roller in an image forming apparatus. [Figure 10] FIG. 10 is a block diagram of a control system that determines whether the pressure is applied or not. [Figure 11] 10 is a flowchart showing an example of determination of pressure contact / separation of a charging roller in an image forming apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0020] [First embodiment] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Fig. 1 is a schematic diagram showing the basic configuration of an image forming apparatus 10 according to the present disclosure.

[0021] As shown in FIG. 1, the image forming apparatus 10 is configured to include a main body 11, a document reading unit 12, a document transport device 13, and a paper feed device 14. The main body 11 has an internal image forming unit for forming (printing) an image on recording paper. The document reading unit 12 is disposed above the main body 11 and reads the document when copying the document. In automatic reading mode, the document transport device 13 sequentially transports documents placed on a document set tray toward the document placement table of the document reading unit 12. The paper feed device 14 has at least one paper feed cassette for stocking recording paper, and separates recording paper one sheet at a time from a selected paper feed cassette and transports it toward the main body 11. The main body 11 forms an image on the recording paper sent from the paper feed device 14.

[0022] Image data handled by image forming apparatus 10 corresponds to a color image using each of the colors black (K), cyan (C), magenta (M), and yellow (Y), or a monochrome image using a single color (e.g., black). For this reason, image forming apparatus 10 has four process units Pa-Pd corresponding to black, cyan, magenta, and yellow as image forming sections. Each process unit Pa-Pd has a photosensitive drum 30a-30d (image carrier: see FIG. 2, etc.), respectively, and forms a toner image corresponding to the image data on the corresponding photosensitive drum 30a-30d using a known electrophotographic process.

[0023] The toner images formed on the photosensitive drums 30a to 30d of each of the process units Pa to Pd are sequentially transferred (primary transfer) onto the intermediate transfer belt 21 and superimposed. As a result, a color toner image is formed on the intermediate transfer belt 21. The color toner image on the intermediate transfer belt 21 is transferred (secondary transfer) onto a recording sheet by the secondary transfer device 15, and the recording sheet is heated and pressed by the fixing unit 16 to fix the color toner image on the recording sheet. Of course, it is also possible to form a monochrome toner image using only the process unit Pa.

[0024] The image forming apparatus 10 has an intermediate transfer unit 20 that is detachable from the main body 11, and the intermediate transfer belt 21 is included in the intermediate transfer unit 20. Fig. 2 is a schematic diagram showing the structure around the intermediate transfer unit 20 when it is attached to the main body 11 (when forming a color image). Fig. 3 is a schematic diagram showing the structure around the intermediate transfer unit 20 when it is being detached.

[0025] As shown in FIG. 2, the intermediate transfer belt 21 is stretched over multiple rollers, and the toner images formed on the photosensitive drums 30a-30d are intermediately transferred onto the surfaces thereof, as described above. The intermediate transfer unit 20 includes the intermediate transfer belt 21, a drive roller 22, a tension roller 23, and intermediate transfer rollers 24a-24d. The drive roller 22, tension roller 23, and intermediate transfer rollers 24a-24d are multiple rollers that stretch the intermediate transfer belt 21, and the drive roller 22 moves and rotates the intermediate transfer belt 21 in a predetermined movement direction F. The tension roller 23 stretches the intermediate transfer belt 21 between itself and the drive roller 22, applying a predetermined tension to the intermediate transfer belt 21 to prevent slack and ensuring that the rotational force of the drive roller 22 is transmitted to the intermediate transfer belt 21. The intermediate transfer rollers 24a-24d are provided at positions inside the intermediate transfer belt 21 corresponding to the photosensitive drums 30a-30d (sometimes collectively referred to as photosensitive drums 30) of the process units Pa-Pd. 2 and 3 show only a portion of the components of the process units Pa-Pd (the photosensitive drums, charging units (charging rollers 31a-31d), developing units (developing devices 33a-33c: sometimes collectively referred to as developing device 33), transfer units, and cleaning units). The exposure device 32 (see FIG. 1), which forms electrostatic latent images on the photosensitive drums 30a-30d by exposing them to light, is provided in common to the process units Pa-Pd.

[0026] 2, only the secondary transfer roller (transfer member) 151 of the secondary transfer device 15 is illustrated. The secondary transfer roller 151 is disposed in a position facing the drive roller 22 with the intermediate transfer belt 21 sandwiched therebetween. The secondary transfer roller 151 is disposed to abut against the surface of the intermediate transfer belt 21 on the drive roller 22 and rotate together with the intermediate transfer belt. The secondary transfer roller 151 pinches and conveys a sheet at a nip portion Np, which is the abutment area with the intermediate transfer belt 21, thereby transferring the toner image intermediately transferred onto the intermediate transfer belt 21 to the sheet. In this embodiment, the secondary transfer device 15 is engaged with a rotary door (not shown) provided on the side of the image forming apparatus 10 (the right side in FIG. 1). As a result, when the door is open, the secondary transfer device 15 also moves, opening the right side of the intermediate transfer unit 20 as shown in FIG. 3, making the intermediate transfer unit 20 detachable from the right side of the main body 11. Although the secondary transfer device 15 according to this embodiment is a roller-type transfer device having a secondary transfer roller 151, it may also be a belt-type transfer device having a secondary transfer belt (transfer member) stretched between the secondary transfer roller 151 and other rollers.

[0027] In the image forming apparatus 10, at least one intermediate transfer roller can be manually switched between being pressed against the photosensitive drum and being separated from it. In this embodiment, in the black (K) process unit Pa, the intermediate transfer roller 24a can be manually switched between being pressed against the photosensitive drum 30a and being separated from it. The position of this black (K) intermediate transfer roller 24a can be manually changed between a first position where the surface of the intermediate transfer belt 21 is in contact with the photosensitive drum 30a, and a second position where the intermediate transfer belt 21 is separated from the photosensitive drum 30a. The switching device that manually changes the position will be described in detail later.

[0028] Meanwhile, in the process units Pb-Pd, the intermediate transfer belt 21 is also switched between being pressed against and separated from the photosensitive drums 30b-30d, but this switching is performed automatically. That is, the intermediate transfer rollers 24b-24d are automatically switched to a position where the intermediate transfer belt 21 is pressed against the photosensitive drums 30b-30d only during color image formation, and to a position where the intermediate transfer belt 21 is separated from the photosensitive drums 30b-30d during monochrome image formation and standby. Figure 4 is a schematic diagram showing the structure around the intermediate transfer unit 20 when it is installed in the apparatus main body (during monochrome image formation and standby), and shows the state where the intermediate transfer belt 21 is separated from the photosensitive drums 30b-30d of the process units Pb-Pd.

[0029] FIG. 5 is a schematic diagram showing the periphery of the intermediate transfer unit 20 with the intermediate transfer rollers 24a to 24d in the second position. The state shown in FIG. 5 is the state when the intermediate transfer unit 20 is attached to or detached from the main body 11 for maintenance or other purposes. By separating the intermediate transfer belt 21 from the photosensitive drums 30a to 30d, the intermediate transfer unit 20 can be attached to or detached from the main body of the image forming apparatus 10 without the intermediate transfer belt 21 rubbing against the photosensitive drum 30a. The intermediate transfer roller 24a is also in the separated state when the image forming apparatus 10 is transported, such as during shipping. This prevents friction between the intermediate transfer belt 21 and the photosensitive drum 30a due to vibrations during transport. After maintenance or installation, a service technician manually switches the separated intermediate transfer roller 24a back to the pressed state. In the state shown in FIG. 5, the intermediate transfer rollers 24b to 24d are automatically separated.

[0030] Because the intermediate transfer roller 24a is manually switched between contact and separation, there is a possibility that the roller may be forgotten to be returned from the separated state to the contact state. When the image forming apparatus 10 is transported, the intermediate transfer roller 24a is left in the separated state and the cabinets (opening and closing doors, etc.) of the image forming apparatus 10 are closed, so it is difficult to notice visually that the intermediate transfer roller 24a has been forgotten to be returned to the contact state. For this reason, the image forming apparatus 10 has a function to determine whether the intermediate transfer roller 24a is contacted or separated (contact / separation determination). This contact / separation determination will be described below.

[0031] The image forming apparatus 10 has an image density sensor 40 (see FIG. 2, etc.), and determines whether the intermediate transfer roller 24a is pressed against or separated from the image forming apparatus 10 by the image density sensor 40. Generally, an image forming apparatus has an image density sensor for performing image density adjustment (so-called process control), and the image density sensor 40 can also serve as the image density sensor used for image density adjustment.

[0032] 2 to 5, the image density sensor 40 is disposed downstream of the intermediate transfer position (i.e., the position where the intermediate transfer roller 24a is disposed) of the process unit Pa and upstream of the secondary transfer position (i.e., the position where the secondary transfer roller 151 is disposed) in the rotation direction of the intermediate transfer belt 21 (the direction of arrow F in FIG. 2). That is, the position of the image density sensor 40 is determined to be a position where the relative position with respect to the intermediate transfer belt 21 changes due to the displacement of the intermediate transfer belt 21 caused by the pressing / separation of the intermediate transfer roller 24a, and a position where the amount of relative displacement is large is preferable. The image density sensor 40 faces the surface of the intermediate transfer belt 21 (the surface onto which the toner image is transferred).

[0033] The intermediate transfer unit 20 may have an opposing roller 25 (see FIG. 2, etc.) positioned opposite the image density sensor 40. The opposing roller 25 moves simultaneously with the intermediate transfer roller 24a when the intermediate transfer roller 24a is manually switched. When the intermediate transfer roller 24a is in a pressure-contact state, the opposing roller 25 approaches the image density sensor 40, and when the intermediate transfer roller 24a is in a separated state, the opposing roller 25 moves away from the image density sensor 40. As a result, when the intermediate transfer roller 24a is in the first position, the opposing roller 25 moves the intermediate transfer belt 21 to a position where the distance between the surface of the intermediate transfer belt 21 and the image density sensor 40 is a predetermined distance. When the intermediate transfer roller 24a is in the second position, the opposing roller 25 moves the intermediate transfer belt 21 to a position where the distance between the surface of the intermediate transfer belt 21 and the image density sensor 40 is greater than the predetermined distance. By providing the opposing roller 25 in the intermediate transfer unit 20, the distance between the intermediate transfer belt 21 and the image density sensor 40 can be accurately adjusted.

[0034] 6 and 7 are schematic diagrams showing an example of a switching mechanism 50 that manually changes the positions of the intermediate transfer roller 24a and the counter roller 25. Fig. 6 shows the case where the intermediate transfer roller 24a is in a pressure-contact state, and Fig. 7 shows the case where the intermediate transfer roller 24a is in a separated state.

[0035] The switching mechanism 50 includes a first bearing member 51, a second bearing member 52, and a link member 53. The first bearing member 51 is an elongated member and is rotatable around a rotation axis 511 located near the center of the longitudinal direction. The first bearing member 51 supports the rotation axis of the intermediate transfer roller 24a at one end of the longitudinal direction, and the other end is connected to the link member 53. The second bearing member 52 is an elongated member and is rotatable around a rotation axis 521 located near the center of the longitudinal direction. The second bearing member 52 supports the rotation axis of the counter roller 25 at one end of the longitudinal direction, and the other end is connected to the link member 53. The second bearing member 52 also includes an operating unit 522 for receiving a manual switching operation by an operator. In this embodiment, the operating unit 522 is shaped like a lever and is provided on the same side as the connection side of the link member 53, but the shape of the operating unit 522 is not particularly limited.

[0036] The intermediate transfer roller 24a can be switched between pressed and separated states by an operator rotating the second bearing member 52 via the operating unit 522. That is, the rotation of the second bearing member 52 is transmitted to the first bearing member 51 via the link member 53, so the first bearing member 51 and the second bearing member 52 rotate simultaneously. For this reason, the intermediate transfer roller 24a can be switched to the separated state by performing the operation from the state shown in FIG. 6 to the state shown in FIG. 7, and the intermediate transfer roller 24a can be returned to the pressed state by performing the reverse operation.

[0037] The switching mechanism 50 is configured to maintain the intermediate transfer roller 24a in a pressed state (the state shown in FIG. 6) and a separated state (the state shown in FIG. 7) using a locking mechanism (not shown) or the like. If the intermediate transfer unit 20 does not include the opposing roller 25, the second bearing member 52 and the link member 53 can be omitted from the switching mechanism 50, and in this case, an operating portion can be provided on the first bearing member 51.

[0038] 8A and 8B are side views of the intermediate transfer belt 21 and the image density sensor 40 as viewed from the drive roller 22 side. In this embodiment, two image density sensors 40 are provided along the width direction (direction perpendicular to the rotation direction) of the intermediate transfer belt 21, but the number of image density sensors 40 is not particularly limited. The image density sensor 40 has a light-emitting unit 41 and a light-receiving unit 42. The light-emitting unit 41 emits light toward the intermediate transfer belt 21, and the light-receiving unit 42 receives the reflected light. Note that FIG. 8A shows the intermediate transfer roller 24a in a pressed state, and FIG. 8B shows the intermediate transfer roller 24a in a separated state.

[0039] FIG. 9 is a flowchart showing an example of contact / separation determination in the image forming apparatus 10. FIG. 10 is a block diagram of a control system that performs contact / separation determination. As shown in FIG. 10, the image forming apparatus 10 has a control unit 60, which controls the light emission of the light emitting unit 41 and the light reception detection of the light receiving unit 42 in the contact / separation determination. The control unit 60 also determines whether the intermediate transfer roller 24a is in contact / separation based on the detection value of the image density sensor 40 (the value of the output signal from the light receiving unit 42). The following contact / separation determination is preferably performed, for example, immediately after the image forming apparatus 10 is powered on.

[0040] 9, first, the image density sensor 40 detects the belt surface of the intermediate transfer belt 21 (S1) without transferring a toner image (toner pattern) to the intermediate transfer belt 21. At this time, the intermediate transfer belt 21 does not need to be rotating.

[0041] In S1, when the intermediate transfer roller 24a is in the first position (pressure contact state), the distance between the intermediate transfer belt 21 and the image density sensor 40 is a predetermined distance. Because the belt surface of the intermediate transfer belt 21 is nearly a mirror surface, light emitted from the light-emitting element 41 is totally reflected by the belt surface of the intermediate transfer belt 21, maximizing the amount of light received by the light-receiving element 42. The light-receiving element 42 outputs an output value (voltage value) corresponding to the amount of received light to the control unit 60. Note that the image density sensor 40 adjusts the light intensity of the light-emitting element 41 so that the output value of the light-receiving element 42 when the intermediate transfer roller 24a is in the pressure contact state is a reference value (e.g., 3 V). Therefore, when the intermediate transfer roller 24a is in the first position, the output value of the light-receiving element 42 is always the reference value and never falls below, for example, 2.7 V, which is a predetermined voltage lower than the reference value.

[0042] On the other hand, when the intermediate transfer roller 24a is in the second position (separated state), the relative position of the intermediate transfer belt 21 with respect to the image density sensor 40 changes compared to the pressed state. For example, the intermediate transfer belt 21 moves away from the image density sensor 40, or the angle of the belt surface at the point facing the image density sensor 40 changes. Both the change in distance and the change in angle significantly reduce the amount of light received by the light receiving unit 42 compared to when the intermediate transfer roller 24a is in the pressed state. As a result, the amount of light received is almost zero in the separated state.

[0043] In S1, it is determined whether the detection value of the image density sensor 40 is within a predetermined determination range. If the detection value is within the determination range, that is, if the detection value of the image density sensor 40 is within a determination threshold range between the determination threshold and the reference value, it is determined that the belt substrate has been detected (detection OK). On the other hand, if the detection value is not within the determination range, that is, if it is not within the determination threshold range between the determination threshold and the reference value, it is determined that the belt substrate has not been detected (detection NG). If the detection is OK in S1, it means that the intermediate transfer belt 21 is close to the image density sensor 40, and it is determined that the intermediate transfer roller 24a is in a pressure contact state. If the detection is NG in S1, it is possible that the intermediate transfer belt 21 is not close to the image density sensor 40, and the process proceeds to step 2. Note that whether the detection value of the image density sensor 40 is within the predetermined determination range can be determined, for example, by comparing the detection value of the image density sensor 40 with a predetermined determination threshold (a value lower than the above-mentioned reference value, for example, 0.3 V). If the detection value is greater than the determination threshold, it is determined that the belt substrate is within the determination range. If the detection value is equal to or less than the determination threshold, it is determined that the belt substrate is not within the determination range.

[0044] In S2, the intermediate transfer belt 21 is rotated idly for a certain distance, and then the image density sensor 40 again detects the belt surface of the intermediate transfer belt 21. If the detection is successful in S2, it is determined that the intermediate transfer roller 24a is in a pressed state. If the detection is unsuccessful in S2, it is determined that the intermediate transfer roller 24a is in a separated state.

[0045] 9, step S2 is provided to eliminate false detections and improve the accuracy of the determination. If the detection is NG in S1, it is possible that a toner image remains on the surface of the intermediate transfer belt 21 even though the intermediate transfer roller 24a is in a pressed state, and the image density sensor 40 detected the remaining toner image, resulting in the detection being NG. The toner image on the surface of the intermediate transfer belt 21 absorbs the light emitted from the light-emitting element 41 (in the case of black toner) or diffusely reflects it (in the case of color toner), and in either case, the amount of light received by the light-receiving element 42 is reduced (resulting in detection being NG).

[0046] Therefore, if detection is NG in S1, it is possible to prevent erroneous detection due to the remaining toner image by performing belt surface detection again in S2 on another surface of the intermediate transfer belt 21. Note that the certain distance over which the intermediate transfer belt 21 is rotated in S2 is preferably a distance that allows the remaining toner image on the intermediate transfer belt 21 to reliably pass the image density sensor 40, and specifically, it is preferably the distance from the intermediate transfer position of the photosensitive drum 30d that is located farthest from the image density sensor 40 to the image density sensor 40.

[0047] However, step S2 is not essential in the present disclosure and can be omitted. When step S2 is omitted, if detection is NG in step S1, it is sufficient to determine that the intermediate transfer roller 24a is in the separated state.

[0048] When the contact / separation determination ultimately determines that the intermediate transfer roller 24a is in the separated state, the image forming apparatus 10 can notify the user that the intermediate transfer roller 24a is in the separated state. In this case, the notification is preferably made by display on the display unit 70 (see FIG. 10) provided in the image forming apparatus 10, but may also be made by sound or other means. Furthermore, when the intermediate transfer roller 24a is in the separated state, the image forming apparatus 10 preferably does not permit the execution of a print job (the formation of a toner image in the process units Pa to Pd) to prevent unnecessary toner consumption.

[0049] As described above, the contact / separation determination in the image forming apparatus 10 of the present disclosure is performed by detecting the belt surface of the intermediate transfer belt 21 in response to changes in the relative positions of the intermediate transfer belt 21 and the image density sensor 40, so there is no need to form a toner image for the determination, eliminating unnecessary toner consumption. Furthermore, since there is no need to perform an intermediate transfer operation of a toner image from the photosensitive drum 30 to the intermediate transfer belt 21 to perform the contact / separation determination, the time required for the determination can be reduced compared to the determination method of Patent Document 1, etc. The image density sensor 40 used for the determination is also the image density sensor used for process control, so there is no increase in the number of parts required for the determination, and no increase in costs.

[0050] Second Embodiment In the image forming apparatus 10 of this embodiment, the charging rollers 31a to 31d (see FIG. 2 and other figures; sometimes collectively referred to as charging roller 31) in each of the process units Pa to Pd are biased by a biasing member to contact the photosensitive drum 30 with a predetermined pressure and rotate together with the photosensitive drum 30. Alternatively, a known contact / separation mechanism may be provided to allow the charging roller 31 to be contacted and separated from the photosensitive drum 30. In the case of a charging roller 31 that is contactable and separable from the photosensitive drum 30, it is preferable that the contact state of the charging roller 31 with respect to the photosensitive drum 30 can be determined. Even in the case of a charging roller 31 that is not contactable and separable, it is preferable that the contact state of the charging roller 31 with respect to the photosensitive drum 30 can be determined because the contact state with the photosensitive drum 30 may be poor. The image forming apparatus 10 can also determine the contact state of the charging roller 31 using the image density sensor 40. Determining the contact state of the charging roller 31 is described below.

[0051] Fig. 11 is a flowchart showing an example of determining the contact state of the charging roller 31 in the image forming apparatus 10. The control flow in Fig. 11 is executed in the process unit Pa immediately after it is determined that the intermediate transfer roller 24a is in the pressure contact state in the control flow in Fig. 9 in the first embodiment. The control flow in Fig. 11 can also be executed in each of the process units Pb to Pd, but in this case, it is executed after the intermediate transfer rollers 24b to 24d are in the pressure contact state.

[0052] 11, first, a confirmation operation is performed in the process unit that performs the confirmation (S11). This confirmation operation includes an image forming operation in which a toner image (a toner pattern for confirmation) is formed on the photosensitive drum, and an intermediate transfer operation to the intermediate transfer belt 21. In this image forming operation, the charging bias in the charging roller 31 and the developing bias in the developing device 33 are normally applied, but the photosensitive drum 30 is not exposed by the exposure device 32. Note that on the photosensitive drum 30, the exposed area becomes the image area, and the non-exposed area becomes the non-image area.

[0053] Next, it is determined whether or not a toner image has been detected by the image density sensor 40 within a specified time (S12). The specified time in this case is, for example, the elapsed time from the start of the checking operation, and is set depending on the process unit that performs the determination.

[0054] When the charging roller 31 is in the contact state, the photosensitive drum 30 is normally charged and is not exposed, so the entire area becomes a non-image area. That is, when no toner image is detected in S12 (NO in S12), the charging roller 31 is determined to be in the contact state.

[0055] On the other hand, if the contact state of the charging roller 31 is poor (for example, if the charging roller 31 is in one-sided contact or the contact pressure is weak and the charging roller 31 is not properly contacted), the photosensitive drum 30 will not be charged normally. As a result, a potential difference occurs between the surface of the photosensitive drum 30 and the developing bias, and a toner image (solid image) is formed on the surface of the photosensitive drum 30 even though the photosensitive drum 30 is not exposed to light. Since the formed toner image is intermediately transferred to the intermediate transfer belt 21, if a toner image is detected in S12 (YES in S12), it is determined that the charging roller 31 is not in contact with the photosensitive drum 30, which is an abnormal state.

[0056] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be determined based on the claims. [Explanation of symbols]

[0057] 10 Image forming device 15 Secondary transfer device 151 Secondary transfer roller (transfer member) 20 Intermediate transfer unit 21 Intermediate transfer belt 22 Drive roller 23 Tension roller 24a~24d Intermediate transfer roller 25 Opposing roller 30a to 30d Photosensitive drum (image carrier) 31a to 31d Charging rollers 32 Exposure equipment 33a~33d Developing device 40 Image density sensor 50 Switching mechanism 60 Control Unit 70 Display section Pa~Pd Process unit (image forming section)

Claims

1. an image forming unit having an image carrier and forming a toner image on the image carrier; an intermediate transfer belt stretched by a plurality of rollers onto which the toner image on the image carrier is intermediately transferred; an intermediate transfer roller, which is one of the plurality of rollers, and whose position can be changed by manual operation between a first position where the surface of the intermediate transfer belt is brought into contact with the image carrier, and a second position where the intermediate transfer belt is separated from the image carrier; an image density sensor that detects a toner image on the intermediate transfer belt, the image density sensor being positioned relative to the intermediate transfer belt when the intermediate transfer roller is at the first position and when the intermediate transfer roller is at the second position; and a control unit that determines whether the intermediate transfer roller is at the first position or the second position based on a detection value of the image density sensor.

2. 2. The image forming apparatus according to claim 1, The image forming apparatus according to claim 1, wherein the control unit does not permit the image forming unit to form a toner image when it determines that the intermediate transfer roller is at the second position.

3. 2. The image forming apparatus according to claim 1, a drive roller, which is one of the plurality of rollers, that moves and rotates the intermediate transfer belt in a predetermined movement direction; a transfer member that is disposed to contact the surface of the intermediate transfer belt on the drive roller and rotate together with the intermediate transfer belt, and that transfers the toner image intermediately transferred onto the intermediate transfer belt onto the sheet by sandwiching and transporting the sheet at a nip portion that is a contact area with the intermediate transfer belt; The image forming apparatus is characterized in that the image density sensor is disposed downstream of the intermediate transfer roller and upstream of the nip portion in the moving direction of the intermediate transfer belt.

4. 2. The image forming apparatus according to claim 1, An image forming apparatus characterized in that it comprises an opposing roller, which is one of the plurality of rollers, positioned opposite the image density sensor, and which, when the intermediate transfer roller is in the first position, moves the intermediate transfer belt to a position where the distance between the surface of the intermediate transfer belt and the image density sensor is a predetermined distance, and, when the intermediate transfer roller is in the second position, moves the intermediate transfer belt so that the distance between the surface of the intermediate transfer belt and the image density sensor is greater than the predetermined distance.

5. 2. The image forming apparatus according to claim 1, the image density sensor includes a light emitting unit that irradiates light toward the intermediate transfer belt, and a light receiving unit that receives light reflected from the intermediate transfer belt and outputs an output signal corresponding to the amount of light received; When determining whether the intermediate transfer roller is at the first position or the second position, The control unit causes the light-emitting unit to emit light, and if the value of the output signal from the light-receiving unit, which is the detection value detected by the image density sensor, is within a predetermined judgment range, determines that the intermediate transfer roller is at the first position, and if the value of the output signal from the light-receiving unit is not within the judgment range, determines that the intermediate transfer roller is at the second position.

6. 2. The image forming apparatus according to claim 1, A display unit is provided, The image forming apparatus is characterized in that, when the intermediate transfer roller is in the second position, the control unit displays on the display unit that the intermediate transfer belt is separated from the image carrier.

7. 2. The image forming apparatus according to claim 1, The image forming unit includes: a charging roller to which a charging bias having a predetermined voltage value is supplied, and which charges the image carrier to a predetermined potential; an exposure device that exposes the image carrier charged to the predetermined potential to form an electrostatic latent image; a developing device containing toner, which develops the electrostatic latent image with the toner when a developing bias having a predetermined voltage value is supplied; The control unit After it is determined that the intermediate transfer roller is at the first position, a charging bias is supplied to the charging roller and a developing bias is supplied to the developing device, but in a state where the exposure device does not expose the image carrier, a confirmation operation is performed, which includes an image forming operation of forming a toner image on the image carrier and an intermediate transfer operation to the intermediate transfer belt; an image forming apparatus characterized in that, if the image density sensor does not detect a toner image within a specified time period during which the confirmation operation is performed, it is determined that the charging roller is in contact with the image carrier, and, if the image density sensor detects a toner image within the specified time period, it is determined that the charging roller is in an abnormal state of not being in contact with the image carrier.

Images