JP6552252B2 - Image forming device - Google Patents

Description

  The present invention relates to an image forming apparatus for forming an image on a sheet.

  In an electrophotographic image forming apparatus, a registration roller feeds a sheet to a transfer unit. At the transfer portion, a toner image formed on an image carrier such as an intermediate transfer belt or a photosensitive drum is transferred to a sheet. The transferred toner image is fixed on the sheet by a fixing device.

  When a toner image is transferred to a sheet at a transfer nip formed by an image carrier (intermediate transfer belt or photosensitive drum) and a transfer unit, the sheet to which the toner image is transferred is not separated from the image carrier, There may be a problem of winding around the image carrier. If the sheet is wound without being separated from the image carrier, the sheet becomes jammed.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses an apparatus that can output and rotate the registration roller by a control unit that outputs an ON / OFF command signal to a registration clutch that blocks transmission of driving force from the motor to the registration roller. When the winding detection sensor detects the paper wound around the circumferential surface of the photosensitive drum, a winding detection signal is sent to the control unit, and the registration clutch is immediately turned off to stop the rotation of the registration roller.

Japanese Patent Laid-Open No. 6-24607

  If the inertia of the image carrier is large, the rotation of the image carrier continues without stopping immediately even if the drive motor for driving the image carrier is stopped based on the detection of the sheet winding. Therefore, the sheet in contact with the image carrier is fed even after detecting the sheet winding and stopping the drive motor of the image carrier. Then, there is a possibility that a problem may occur in which the sheet is sent to a place where it is difficult to perform jam processing. Further, depending on the position of the cleaning unit for cleaning the image carrier, the cleaning unit may be damaged by the fed sheet.

  In the configuration in which the registration roller is separated during transfer, even if the above-described known technique for blocking the drive of the registration roller is applied, the above problem caused by the sheet being fed by the image carrier rotating by inertia can not be prevented. .

  Here, one of the reasons for separating the registration roller during transfer to a sheet is exemplarily introduced. In recent years, the registration roller has been moved (shifted) in the direction perpendicular to the sheet conveyance direction to meet the demands for high productivity, space saving, and high-precision image position accuracy. A mechanism to perform has been devised. This mechanism is employed particularly in high-speed and high-precision devices.

  The sheet position is detected, and the shift amount of the registration roller is determined according to the detected sheet position. Here, after the shift, it is necessary to return the registration roller to the home position in preparation for the next sheet. However, if the interval between sheets (sheet spacing) during continuous sheet passing is small, it may be difficult in terms of time to perform the operation of returning the registration roller to the home position only by the time between sheets.

  Therefore, a separating mechanism for separating the nip of the registration roller is provided in the image forming apparatus. Then, the nip of the registration roller is separated and moved to the home position while the sheet passes through the registration roller nip.

In the image forming apparatus according to the present invention , a sheet is held by an image carrier and the image carrier, and a transfer unit for transferring a toner image formed on the image carrier to the sheet; and rotationally driving the image carrier A drive unit to
A pair of rollers including a first roller and a second roller disposed upstream of the transfer unit in the sheet conveyance direction and conveying the sheet to the transfer unit, the first roller, and the second roller A change unit that changes the state of the roller pair to a sandwiching state for sandwiching and a separated state in which the first roller and the second roller are separated, and the sheet carried by the roller pair is the image bearing in situ of sheets nipped the body and the transfer section and the image bearing member or after sandwiched by the by said transfer unit is conveyed, the state of the roller pair to said separated state A control unit for controlling the change unit, the control unit stopping the drive unit in response to occurrence of sheet conveyance abnormality, and holding the state of the roller pair from the separated state Condition and Controlling the changing portion so that, the control section is separated the transfer unit from said image bearing member when the conveyance failure of the sheet occurs, the roller pair is said from the separated state and the image bearing member The control unit is configured to cause the roller pair, which has been changed in response to occurrence of the conveyance abnormality from the separated state to the sandwiched state, to be in the separated state again so that the transfer unit is in the separated state. The change unit is controlled .

  According to the present invention, it is possible to improve the jam handling performance.

FIG. 1 is a schematic view of an image forming apparatus according to an embodiment of the present invention. The perspective view of a registration unit. Correspondence list of sheet size, sheet basis weight, and registration roller shift operation availability between sheets. Control block diagram. The figure explaining the operation | movement at the time of the separation defect in 1st Embodiment. The flowchart in 1st Embodiment. Schematic which shows the control flow at the time of the separation defect in 2nd Embodiment. The flowchart in 2nd Embodiment.

First Embodiment
(Configuration of the entire image forming apparatus)
FIG. 1 shows a schematic cross-sectional view of a color digital printer as an example of an image forming apparatus according to the present invention.

  The surface of the four photosensitive drums 101a to 101d provided in the image forming apparatus is uniformly charged by the charging rollers 102a to 102d. Image signals of yellow (Y), magenta (M), cyan (C), and black (K) are input to the laser scanners 103a to 103d, respectively, and the drum surface is irradiated with laser light according to the image signals to charge them. To form a latent image.

  The latent images formed on the photosensitive drums are developed with toners of yellow, magenta, cyan and black by developing units 104a to 104d. The toners developed on the respective photosensitive drums are sequentially transferred to the intermediate transfer belt 106, which is an endless belt-like image carrier, by the primary transfer rollers 105a to 105d, and a full-color toner image is formed on the intermediate transfer belt 106. The

  A sheet fed from one of the sheet feeding cassettes 111 and 112 as the sheet feeding unit is conveyed toward the registration roller pair 120 by the conveyance roller pair 114 and the conveyance roller pair 115. The sheet is also conveyed to the registration roller pair 120 from the manual feeding unit 113.

  The registration roller pair 120 aligns the conveyed sheet with the toner image. Details of control in the registration roller pair 120 will be described later.

  The toner image on the intermediate transfer belt 106 is transferred onto a sheet by a secondary transfer outer roller (transfer roller) 109. The toner image transferred to the sheet is fixed to the sheet by being heated and pressed by the fixing device 110. Thereafter, the sheet is discharged from the discharge portion 119a or 119b to the outside of the apparatus main body. The secondary transfer outer roller 109 as a transfer unit is configured to be able to contact and separate from the intermediate transfer belt 106, and separates the nip at the time of jam processing or the like.

  From the operation unit 200 (see FIG. 4) provided in the image forming apparatus, the user can input various information (size information, basis weight information, surface property information, etc.) relating to the sheet to the controller 50 (control unit) described later. Is set to Further, the computer 201 connected via the network is set so that various information related to the sheet can be input to a controller 50 (control unit) described later.

  The paper feed cassettes 111 and 112 are provided with size detection means 130 (see FIG. 4) for detecting the size of the stored sheets and causing the controller 50 (control unit) of the image forming apparatus to recognize the size. The size detection means 130 has a rotatable size detection lever that slides and interlocks with a side regulating plate that regulates the position in the width direction of the sheet. The side regulating plate is movable in accordance with the side edge of the sheet, and the position of the sheet in the width direction can be adjusted with respect to the image forming unit.

  The size detection unit 130 includes a plurality of sensors or switches provided at positions corresponding to the size detection levers in the mounting portion of the apparatus main body in which the sheet feeding cassettes 111 and 112 are mounted. Therefore, when the side regulating plate is moved according to the side edge of the sheet, the size detection lever is interlocked and pivoted. When the paper feed cassettes 111 and 112 are attached to the image forming apparatus, the size detection lever selectively turns ON / OFF the sensor or the switch detection element arranged in the attachment portion of the apparatus main body. Thereby, signals of different patterns are sent from the sensor or the switch to the controller 50. Then, the controller 50 can recognize the size of the sheet stored in the paper feed cassette based on the signal. A similar mechanism may be provided in the manual feed unit 113 as a size detection mechanism.

  The side regulating plate has a function of preventing sheet skew and lateral registration deviation (position deviation in the width direction) that occur during sheet feeding. However, in reality, if a slight gap is generated between the side regulating plate and the sheet, the skew of the sheet and the lateral displacement may occur. Further, the sheet fed from the paper feed cassettes 111 and 112 may be skewed and laterally misaligned during conveyance.

  Therefore, the image forming apparatus of the present embodiment corrects the skew of the conveyed sheet by the registration roller pair 120. In other words, the leading edge of the conveyed sheet is brought into contact with the nip portion of the stopped pair of registration rollers 120, and the leading edge of the sheet is moved along the nip portion while forming a loop on the sheet, and the sheet is skewed. to correct. At this time, the loop amount formed on the sheet needs to ensure that the leading edge of the sheet contacts the nip portion of the registration roller pair 120 and the leading edge of the sheet follows the nip portion. Therefore, the loop amount is set by feeding a predetermined amount of sheet by the conveyance roller pair 115 disposed upstream of the registration roller pair 120 after the sheet passes through the registration sensor 141 (see FIG. 2). The

  Between the registration roller pair 120 and the secondary transfer portion 118, a CIS 143 as position detection means for detecting the position in the width direction of the sheet is disposed. After conveyance of the sheet is started by the registration roller pair 120, the detection result (the position of the detected sheet) by the CIS 143, the nominal position, and the deviation amount are calculated as the lateral registration correction amount. The lateral registration position (position in the width direction) of the sheet is corrected by shifting the registration roller pair 120 holding the sheet in the thrust direction by the lateral registration correction amount. Here, the thrust direction is the width direction of the sheet orthogonal to the sheet conveyance direction.

  FIG. 2 illustrates a sheet conveying device 116 that is provided in the middle of a sheet conveying path that connects the sheet feeding cassettes 111 and 112 and the secondary transfer unit 118 and performs sheet skew correction and position adjustment in the sheet width direction. It is a perspective view.

  In the conveying roller pair 115, an upper roller 115a having a roller made of polyacetal (POM) and a lower roller 115b formed of a rubber roller are disposed to face each other. The upper roller 115a is swingably supported by a lever or the like, and is pressed against the lower roller 115b by the elastic force of a spring (not shown).

  A registration roller pair 120 provided downstream of the conveying roller pair 115 and abutting against the leading edge of the sheet conveyed to correct the skew of the sheet is an upper roller as a first roller and a second roller as a second roller. It has a lower roller. By bringing the sheet into contact with the nip portion between the upper roller and the lower roller of the registration roller pair 120 so that the front end of the sheet is aligned, the skew of the sheet is corrected.

  The upper roller of the registration roller pair 120 has a roller made of polyacetal (POM), the lower roller is formed of a rubber roller, and the upper roller and the lower roller are arranged to face each other. The upper roller is movably supported, and the upper roller is in pressure contact with the lower roller by the elastic force of the spring.

  In FIG. 2, reference numeral 62 denotes a roller driving motor for driving the first lower roller 115 b of the conveying roller pair 115. Reference numeral 61 denotes a registration drive motor 61 for driving the lower roller of the registration roller pair 120.

  Upper guides 66 and 67 and a lower guide 68 for guiding the sheet to be conveyed are disposed between the conveying roller pair 115 and the registration roller pair 120. The upper guides 66 and 67 and the lower guide 68 are partially spaced from each other, and are configured to allow a loop formed by the sheet that is abutted against the nip portion of the registration roller pair 120.

  The mechanism for shifting the sheet in the thrust direction is as follows. The lower roller of the registration roller pair 120 is fixed to the roller rotation shaft. The roller rotation shaft is fixed to the apparatus main body so as to be movable in the width direction of the sheet. As the roller rotation shaft moves in the sheet width direction, the upper roller and the lower roller move together in the sheet width direction.

  The pinion gear 44 is rotated by a driving force from a registration roller shift motor (hereinafter referred to as a shift motor) 43 to translate the rack 45. The rack 45 is rotatable in the rotational direction with respect to the roller rotation axis of the lower roller of the registration roller pair 120, and is fixed and supported in the thrust direction. Thereby, the thrust movement of the registration roller pair 120 is enabled, and the sheet nipped by the registration roller pair 120 can be shifted in the width direction.

  The registration roller idler gear 63 has a wider tooth width than the registration roller input gear 64. This is for maintaining the meshing of the gear and enabling the rotation of the registration roller pair 120 even when the registration roller pair 120 and the registration roller input gear 64 are thrust.

  As described above, position detection in the sheet width direction is performed by the CIS 143. The arrangement of the CIS 143 is upstream in the conveyance direction with respect to the image transfer unit in the sheet material conveyance direction.

  The separation operation of the registration roller pair 120 is performed by raising the upper roller of the registration roller pair 120 by the separation levers 142 f and 142 r. Separation levers 142f and 142r are fixed at two locations on the shaft 146, and a drive input gear 144 is fixed at one shaft end. The counterclockwise rotation of the separation motor 145 rotates the shaft 146, and the separation levers 142f and 142r are rotated clockwise by a predetermined amount. Then, the separation operation of the registration roller pair 120 is completed. That is, the upper roller and the lower roller of the registration roller pair 120 are separated. The separation levers 142 f and 142 r and the separation motor 145 constitute a changing unit that changes the state of the registration roller pair 120 into the separated state and the sandwiched state. The separated state of the registration roller pair 120 is a state in which the upper roller and the lower roller of the registration roller pair 120 are separated. The sandwiched state of the registration roller pair 120 is a state in which the upper roller and the lower roller are pressed against each other so that the upper roller and the lower roller of the registration roller pair 120 sandwich the sheet.

  When the upper roller of the registration roller pair 120 is brought into pressure contact, the separation motor 145 is rotated in the direction opposite to that at the time of separation to release the contact between the separation levers 142f and 142r and the shaft of the upper roller. Then, the upper roller and the lower roller are pressed against each other by the force of the spring for pressing the upper roller and the lower roller of the registration roller pair 120, and the pressing operation is completed. In the following description, the press-contact operation for pressing the upper roller and the lower roller of the registration roller pair 120 is also referred to as “attaching operation”.

  In the present embodiment, control for shifting the registration roller pair 120 by a predetermined amount is performed in order to correct the lateral registration position of the sheet. Control for shifting the registration roller pair 120 is performed for each sheet. Therefore, in the case of a continuous job, it is necessary to return the thrust position of the registration roller pair 120 to the central position (home position) before the sheet subsequently conveyed to the preceding sheet reaches the registration roller pair 120. . The operation of returning the shifted registration roller pair 120 to the central position (home position) in the thrust direction is hereinafter referred to as "home position operation".

  It is preferable that the home position operation be completed in the time between sheets not nipping the sheet, but in order to achieve the high productivity of the apparatus required for the recent image forming apparatus especially, the sheet interval is as small as possible It is required to do. In order to achieve high productivity, the time between sheets may be shorter than the time required for home position operation.

  In many image forming apparatuses, the time between sheets is proportional to the length in the sheet conveyance direction and the sheet basis weight. Depending on the sheet size and basis weight, the home position operation between the sheets may not be in time. FIG. 3 shows a table showing the relationship between the standard sheet size and sheet basis weight and whether the home position operation is in time between sheets. In the case of the sheet size and sheet basis weight indicated by x in this table, the registration roller pair 120 is separated and the home position operation is performed before the trailing edge of the preceding sheet passes the registration roller. .

  The necessity of separating the registration roller pair 120 has been described above in terms of the productivity of the apparatus. Next, as another purpose of separating the registration roller pair 120, an aspect of improving the positional accuracy of the image will be described. During the image transfer, when the sheet is conveyed at the nip between the secondary transfer nip and the registration roller pair 120, the sheet may be bent at the secondary transfer nip, and the image transferred to the sheet may be distorted. This is caused by misalignment of the secondary transfer nip and the registration roller pair nip with respect to the sheet conveying direction. Therefore, it is desirable for the sheet being subjected to the secondary transfer to have no influence on the sheet conveyance as much as possible.After the sheet reaches the secondary transfer nip, the registration roller pair 120 is separated, It becomes possible to improve the position accuracy of the image. That is, the form which performed the home position operation | movement by moving the registration roller pair 120 to the width direction was illustrated. However, the present invention is also applicable to the case where the movement of the registration roller pair 120 in the width direction is not performed (the registration roller pair 120 is separated only to improve the positional accuracy of the image).

  The necessity of the attachment / detachment control of the registration roller pair 120 has been described above from the viewpoint of high productivity and high position accuracy. In the present embodiment, control is performed to separate the registration roller pair 120 after the leading edge of the sheet reaches 10 mm downstream of the secondary transfer nip regardless of the size and basis weight of the sheet.

  Here, in the secondary transfer unit 118 that performs image transfer from the intermediate transfer belt 106 to the sheet, there is a problem that the sheet does not separate from the intermediate transfer belt 106 due to electrostatic adsorption force (separation failure). is there. In particular, it is difficult to prevent the occurrence of a phenomenon because the phenomenon is affected by the moisture content of the sheet, the curl state, the deterioration state of the components of the apparatus, etc. Coupled with the recent demand for thin paper support for devices, it has become a major issue.

  In the present embodiment, whether or not the sheet separation at the secondary transfer unit 118 has been normally performed is determined by the sheet detection sensor 151 provided downstream of the secondary transfer unit 118. Therefore, if the sheet detection sensor 151 does not detect the sheet at a predetermined timing, it is determined that the secondary transfer unit 118 has a separation failure (jam or conveyance abnormality), and the intermediate transfer belt 106 and each conveyance roller are stopped. A separation control of the secondary transfer outer roller 109 is performed. In the present embodiment, when the sheet is delayed by 30 mm from the timing of the call for passing the sheet detection sensor 151, it is determined that the sheet is jammed (a 30 mm jam margin is taken). The rotation of the intermediate transfer belt 106 is stopped by the controller 50 stopping the intermediate transfer belt drive motor 49 (drive unit, see FIG. 4) that drives the intermediate transfer belt 106 to rotate.

  Here, the structure including the intermediate transfer belt 106 and the intermediate transfer belt 106 has a large inertia as compared with the conveyance roller and the like. Accordingly, it takes time until the intermediate transfer belt 106 actually stops after receiving the stop control signal (that is, after it is determined that a jam has occurred). In the present embodiment, it takes 1 second to stop the intermediate transfer belt drive motor 49 after it is determined to be jammed and to stop the intermediate transfer belt 106 completely. When a separation failure occurs, the registration roller pair 120 is already separated. In a sheet having a size shorter than 250 mm obtained by adding a jam margin of 30 mm to the distance from the conveying roller pair 115 to the secondary transfer unit 118 (220 mm in this embodiment), the registration roller pair 120 is separated. Therefore, only the secondary transfer unit 118 holds the sheet at the moment when the jam occurs. Then, after the jam is determined, the sheet is conveyed for 1 sec while the sheet is stuck to the intermediate transfer belt 106. Note that, for a sheet having a size longer than 250 mm, the time required for stopping the conveying roller pair 115 is shorter than the time required for stopping the intermediate transfer belt 106 (0.01 sec), so the sheet stops at that timing. In this embodiment, the sheet conveyance speed when an image is transferred to a sheet is 350 mm / s, and the sheet is fed by about 300 mm before the intermediate transfer belt 106 is completely stopped after the jam is determined.

  A cleaning unit 108 for cleaning the transfer residual toner on the intermediate transfer belt 106 is provided downstream of the secondary transfer unit 118 at a position 200 mm from the secondary transfer unit 118. The cleaning unit 108 is a unit that presses an elastic cleaning blade against the intermediate transfer belt 106 to scrape off the toner on the intermediate transfer belt 106, and transports the scraped toner collected by a screw.

  As described above, a sheet having a length of 250 mm or less in the conveyance direction is fed while being adhered to the intermediate transfer belt 106 by another 300 mm after it is determined as a jam when separation failure occurs. Therefore, the leading edge of the sheet may squeeze into the cleaning unit 108, which may cause damage to the cleaning unit 108, scattering of the collected toner in the cleaning unit 108, and the like. In addition, it is necessary to take out the jammed paper that has entered the cleaning unit 108, leading to a significant deterioration in jam handling performance.

  Therefore, in the present embodiment, the registration roller pair 120 is brought into a pressure contact state when it is determined that a separation failure jam has occurred. Then, the sheet is prevented from being moved while being stuck to the intermediate transfer belt 106 together with the intermediate transfer belt 106 rotating by inertia, by the registration roller pair 120 in the pressure contact state.

  Hereinafter, the control flow of the embodiment will be described with reference to FIGS. 5 and 6. FIG. 4 is a control block diagram, and the following operation is executed by the controller (control unit) 50 controlling each motor and the like according to a program stored in the storage unit. The secondary transfer outer roller separation motor in FIG. 4 is a motor for separating the secondary transfer outer roller 109 from the intermediate transfer belt 106.

  In order to align the image on the intermediate transfer belt 106 and the sheet, the registration roller pair 120 starts conveying the sheet at a predetermined timing. When the leading edge of the sheet P (FIG. 5A) conveyed by the registration roller pair 120 reaches a position 10 mm downstream from the secondary transfer unit 118, the registration roller pair 120 is separated (FIG. 5). 5 (2), S101). Simultaneously with the completion of separation of the registration roller pair 120, the rotational drive of the registration roller pair 120 is stopped (S102).

  The controller 50 determines whether or not the sheet detection sensor 151 detects a sheet within a predetermined time (S103). In this embodiment, the predetermined time is a time for starting measurement after the registration roller pair 120 starts conveying the sheet. If the leading edge of the sheet P wraps around the intermediate transfer belt 106 and the sheet detection sensor 151 can not detect the sheet even after the predetermined timing, the controller 50 determines that a jam (separation failure in the secondary transfer portion 118) ( S104). If the sheet is detected, the sheet is conveyed to the downstream process as usual. If it is determined that the separation is defective, the controller 50 stops the driving of the intermediate transfer belt 106, separates the secondary transfer outer roller 109 from the intermediate transfer belt 106, and brings the registration roller pair 120 into a pressure contact state. (FIG. 5 (3), S105). Here, the attaching operation for bringing the registration roller pair 120 into the pressure contact state is performed by the controller 50 controlling the separation motor 145. The secondary transfer outer roller 109 separates from the intermediate transfer belt 106 at the same time as being judged as a jam. Therefore, the clamping force of the registration roller pair 120 is stronger than the force with which the sheet is adhered to the intermediate transfer belt 106 and conveyed, and the sheet is not conveyed with the intermediate transfer belt 106. The time required for the operation of attaching the registration roller pair 120 and the operation of separating the secondary transfer outer roller from the intermediate transfer belt 106 are the same.

  In the present embodiment, the timing of stopping the driving of the registration roller pair 120 is the timing after the registration roller pair 120 is separated. However, when it is determined that a jam has occurred, the driving may be stopped simultaneously with the timing of the attachment operation of the registration roller pair 120. Also in this case, the time required for stopping the driving is shorter than the time required for the landing operation of the registration roller pair 120. Therefore, the sheet is not conveyed by the registration roller pair 120.

  The main control for preventing the movement of the sheet by the arrival operation of the registration roller pair 120 is whether or not the sheet is held in time by the arrival operation of the registration roller pair 120 in a sheet having a short conveyance direction length. For example, the minimum size B5 (182 mm) in the device of this embodiment is as follows.

(1) Distance from the registration roller pair 120 to the secondary transfer portion 118: 100 mm
(2) Distance from secondary transfer unit 118 to sheet detection sensor 151: 30 mm
(3) Distance from detection timing of admonition to judgment of jam (jam margin): 30 mm
(4) Distance traveled by sheet during registration roller pair 120 operation: 15 mm
The sum of (1) to (4) is 175 mm. That is, also in the B5 size, the attachment operation of the registration roller pair 120 after detection of the separation failure jam is in time.

  The registration roller pair 120 is separated again after a predetermined time (a time until the intermediate transfer belt 106, which has been rotating by inertia, stops in this embodiment: 1 sec) after being judged as a jam, (FIG. 5 (4), S106). Here, the reason for the separation is to improve the jam handling performance when the user performs the jam handling. That is, when the registration roller pair 120 is separated, the jam processing performance is better than taking out the sheet from the state where the registration roller pair 120 is nipped by the roller nip.

  As described above, in the configuration in which the registration roller pair 120 is separated when the sheet reaches the secondary transfer unit 118, when the separation failure is detected in the secondary transfer unit 118, the registration roller pair 120 is attached. It is possible to prevent the sheet from being conveyed along with the intermediate transfer belt 106 by the registration roller pair 120 that has been nipped by the attaching operation. Thus, the apparatus can be prevented from being damaged and jamming can be improved.

Second Embodiment
In the first embodiment, when the separation failure jam in the secondary transfer portion 118 occurs, the registration roller pair 120 is attached. As a result, the sheet is prevented from being conveyed along with the intermediate transfer belt 106 by the nipping force of the registration roller pair 120. The second embodiment is different from the first embodiment in that an operation for improving the jam handling property is further added. In the following, the description of the same configuration as that of the first embodiment will be omitted, and matters different from the first embodiment will be described.

  At the time of jam processing, the drawer unit including the registration roller pair 120, the secondary transfer outer roller 109, and the fixing device 110 is pulled out toward the front of the apparatus, thereby taking out the sheet in the apparatus. At this time, the intermediate transfer unit provided with the intermediate transfer belt 106 remains in the apparatus and is separated from the drawer unit. If the leading edge of the sheet is attached to the intermediate transfer belt 106, the following problems may occur. That is, when pulling out the drawer unit, the leading edge side and the trailing edge side of the sheet are pulled to each other, and the posture of the sheet is disturbed, the sheet is broken or broken, and the inside of the apparatus is scattered by unfixed toner on the sheet. Cause jams, etc.

  Therefore, in the second embodiment, after the attachment operation of the registration roller pair 120, the registration roller pair 120 is reversely rotated. Then, by performing control to separate the leading end of the sheet from the intermediate transfer belt 106, the sheet is prevented from being broken or broken and scattering toner is generated when the drawer unit is pulled out.

  The registration drive motor 61 can rotate forward and backward, whereby the registration roller pair 120 can rotate in the sheet conveying direction and in the reverse direction.

  The operation explanatory diagram of FIG. 7 in the present embodiment will be described below with reference to the flowchart of FIG. The operation described below is executed by the controller 50 controlling each motor and the like according to a program stored in the storage unit.

  Here, since S201 to S205 in FIG. 8 are the same as S101 to S105 in the first embodiment, the description will be omitted.

  The controller 50 drives the registration drive motor 61 in the reverse direction after a predetermined time (a time until the intermediate transfer belt actually stops) after being judged as a jam. By this operation, the end of the sheet is conveyed to a predetermined position upstream of the secondary transfer portion 118 in the normal conveyance direction (FIG. 7 (1), S206 in FIG. 8). In the present embodiment, the sheet is conveyed by the reverse rotation of the registration roller pair 120 until the leading end of the sheet is 20 mm upstream from the secondary transfer unit 118. Add the distance (30 mm) from the secondary transfer unit 118 to the sheet detection sensor 151, the jam margin (20 mm), and the distance (20 mm) that the sheet travels during the time required for the registration roller pair 120 to move. The sheet is conveyed in the reverse direction for 90 minutes.

  After conveyance of the leading end of the sheet is completed to a predetermined position (FIG. 7 (2)), the reverse rotation drive of the registration roller is stopped. Then, the registration roller is separated again (FIG. 7 (3), S207 in FIG. 8). The reason for separating the registration roller pair 120 here is the reason described in the first embodiment.

  Here, in S206, when the registration roller pair 120 is rotated in the reverse direction and the sheet is conveyed in the reverse direction, the following phenomenon may occur. That is, depending on the sheet size and the distance relationship between the registration roller pair 120 and the conveyance roller upstream thereof, a loop is generated in the sheet between the registration roller pair 120 and the conveyance roller pair 115. When the registration roller pair 120 is separated in S207, the sheet loop generated between the registration roller pair 120 and the conveyance roller pair 115 is released, and the leading edge of the sheet again moves to the secondary transfer unit 118. A moving phenomenon occurs.

  The reverse rotation of the registration roller pair 120 weakens the electrostatic attraction of the sheet to the intermediate transfer belt 106 once the sheet is separated from the intermediate transfer belt 106. Therefore, the possibility of the sheet sticking to the intermediate transfer belt 106 again is small. However, in view of the possibility of the sheet sticking to the intermediate transfer belt 106, the conveying roller pair 115 upstream of the registration roller pair 120 is configured to be able to rotate forward and backward like the registration roller pair 120. Then, the rotation control of the conveyance roller pair 115 may be performed in synchronization with the forward / reverse rotation control of the registration roller pair 120.

  In any of the first and second embodiments, the method of detecting the winding around the intermediate transfer belt 106 using the sheet detection sensor 151 as the detection of the conveyance abnormality is illustrated. However, if a conveyance abnormality is detected based on another sensor in another conveyance path in the image formation, the intermediate transfer belt 106 may be stopped and the registration roller pair 120 may be attached.

  As described above, when a conveyance abnormality such as a separation failure occurs in the secondary transfer unit 118, the attaching operation of the registration roller pair 120 is performed. Further, the pair of registration rollers 120 is reversely rotated to convey the leading end of the sheet to the upstream of the secondary transfer portion 118, whereby the jam clearance can be improved.

49 Intermediate transfer belt drive motor 50 Controller 106 Intermediate transfer belt 109 Secondary transfer outer roller 120 Registration roller pair

Claims (8)

And the image bearing member,
A transfer unit configured to sandwich a sheet with the image carrier and transfer a toner image formed on the image carrier to the sheet;
A drive unit that rotationally drives the image carrier;
A pair of rollers including a first roller and a second roller, disposed upstream of the transfer unit in the sheet conveyance direction, and conveying the sheet to the transfer unit;
A change unit that changes the state of the roller pair to a holding state for holding a sheet by the first roller and the second roller, and a separated state in which the first roller and the second roller are separated. ,
In situ the sheet conveyed by the roller pair sheets held between said image bearing member and the transfer section and the image carrier and the transfer portion or after sandwiched by is conveyed, the A control unit that controls the changing unit to bring the roller pair into the separated state;
The control unit controls the change unit to stop the drive unit and change the state of the roller pair from the separated state to the nipping state in response to occurrence of sheet conveyance abnormality .
The control unit separates the transfer unit from the image carrier when sheet conveyance abnormality occurs.
The control unit is changed in response to occurrence of the conveyance abnormality from the separated state to the sandwiched state so that the roller pair is in the separated state and the transfer portion is separated from the image carrier. An image forming apparatus , wherein the changing unit is controlled such that the roller pair is in the separated state again . And a detection sensor disposed downstream of the transfer unit in the sheet conveyance direction and detecting the conveyed sheet.
The image forming apparatus according to claim 1, wherein the control unit controls the changing unit to change the state of the roller pair from the separated state to the sandwiching state according to a signal from the detection sensor. . A moving means for moving the roller pair in the width direction of the sheet perpendicular to the sheet conveying direction;
After moving the roller pair holding the sheet by the moving means in the width direction, the changing unit changes the state of the roller pair to the separated state;
The image forming apparatus according to claim 1, wherein the moving unit moves the roller pair to a predetermined position when the roller pair is in the separated state. Having position detecting means for detecting the position in the width direction of the conveyed sheet;
The control unit controls the moving unit to move the roller pair holding the sheet from the predetermined position in the width direction based on the detection result of the position detection unit. The image forming apparatus described in 1. 5. The roller pair according to any one of claims 1 to 4 , wherein the roller pair is rotated in the direction opposite to the sheet conveyance direction after the roller pair is brought into the nipping state in response to occurrence of the conveyance abnormality. The image forming apparatus described in 1. A sheet conveying unit disposed upstream of the roller pair in the sheet conveying direction and configured to convey a sheet to the roller pair;
6. The sheet conveying device according to claim 5 , wherein the sheet conveying unit is driven to convey the sheet in the direction opposite to the sheet conveying direction when the roller pair is rotationally driven in the direction opposite to the sheet conveying direction. Image forming apparatus.   The image forming apparatus according to any one of claims 1 to 6, wherein the image carrier is an intermediate transfer belt to which a toner image is transferred from a photosensitive member. A pair of rollers including a first roller and a second roller, and nipping and conveying the sheet between the first roller and the second roller;
An intermediate transfer belt onto which a toner image is transferred from a photoreceptor;
A transfer roller which nips and conveys a sheet with the intermediate transfer belt, and transfers the toner image transferred to the intermediate transfer belt to the sheet fed from the pair of rollers;
A moving means for moving the pair of rollers in the sheet width direction orthogonal to the sheet conveying direction; a holding state in which the sheet is held by the first roller and the second roller; the first roller and the second roller A changing unit that changes the state of the roller pair to a separated state in which
Position detecting means for detecting the position of the conveyed sheet in the width direction;
After the moving unit moves the pair of rollers holding the sheet from the predetermined position in the width direction based on the detection result of the position detecting unit, the sheet is the intermediate transfer belt and the transfer roller. After being nipped, the change unit changes the state of the roller pair to the separated state,
Causing the moving means to move the roller pair to the predetermined position when the roller pair is in the separated state;
At least when the sheet is nipped by the intermediate transfer belt and the transfer roller, the change unit changes the state of the roller pair from the separated state to the nipping state in response to occurrence of sheet conveyance abnormality. ,
A control unit;
I have a,
The control unit separates the transfer roller from the intermediate transfer belt when sheet conveyance abnormality occurs.
The control unit is changed in response to occurrence of the conveyance abnormality from the separated state to the sandwiched state so that the roller pair is in the separated state and the transfer roller is separated from the intermediate transfer belt. An image forming apparatus , wherein the changing unit is controlled such that the roller pair is in the separated state again .

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