JP2013064961A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique which allows a user to easily pull out a recording material when a jam has occurred in which a tip of the recording material is wound one turn or more around a fixing roller 1 in a fixing device.SOLUTION: An image forming apparatus comprises: fixing means which includes a pressure roller and a fixing roller and which fixes an unfixed toner image on a recording material by sandwiching the recording material at a nip part formed by the pressure roller and the fixing roller, and heating the recording material; conveyance means which conveys the recording material switching the conveyance direction of the recording material in the fixing means to either the forward direction which is the conveyance direction of the recording material when the image formation is normally performed, or the reverse direction; jam detection means which detects a jam generation of the recording material; and control means which controls the conveyance means so that the recording material is conveyed in the reverse direction for a predetermined distance when the jam generation is detected by the jam detection means.

Description

  The present invention relates to an electrophotographic image forming apparatus.

An electrophotographic image forming apparatus has a fixing device that fixes a toner image formed on a sheet by heat and pressure. In general, this fixing device has a pair of fixing rollers including a fixing roller and a pressure roller, and each roller is provided with a heater.
During printing, a paper jam (hereinafter referred to as jam) may occur around the nip portion of the fixing roller pair. The jam of the fixing device includes an accordion jam that causes the paper to be in an accordion shape, and a wrap jam that wraps around the fixing roller. In order to check whether or not the sheet has normally passed through the nip of the fixing roller pair of the fixing device, a sensor (hereinafter referred to as a paper discharge sensor) may be disposed at the outlet of the fixing device. Here, since the vicinity of the nip portion of the fixing roller pair becomes high temperature due to the heat of the heater inside the fixing roller, it is difficult to dispose the paper discharge sensor in the vicinity of the nip portion of the fixing roller pair. It is necessary to arrange a paper discharge sensor. Then, when the paper discharge sensor detects that the paper does not normally pass through the fixing device, the paper may already be wound around the fixing roller. When such a jam occurs, it is necessary for the user to perform jam processing by pulling out the paper. In Patent Document 1, the fixing roller and the pressure roller are separated from each other when a jam occurs, thereby reducing the force required for the user to pull out the paper during the jam processing so that the user can easily perform the jam processing. A method has been proposed.

JP 2008-139676 A

If the leading edge of the sheet winds around the fixing roller for one turn or more, the toner may be fused at a portion where the sheet overlaps, and in this case, the user cannot easily pull out the sheet. In order to detect the occurrence of a jam before the leading edge of the sheet winds around the fixing roller for more than one turn, it is necessary to dispose a paper discharge sensor so that the following equation is satisfied.
Distance between fixing nip and paper discharge sensor <Fixing roller diameter x π
However, in recent years, the size of the fixing device has been reduced, and the diameter of the fixing roller has been reduced. Therefore, the position where this formula is satisfied is close to the nip portion of the fixing roller pair, and the influence of the heat of the fixing roller. Considering this, it is difficult to arrange the paper discharge sensor.

  The present invention provides a technique for facilitating a jam processing operation by a user in an image forming apparatus in which the leading edge of a recording material can be wound around the fixing roller one or more times when occurrence of a jam is detected. With the goal.

The present invention has a pressure roller and a fixing roller, and fixes the unfixed toner image on the recording material by sandwiching and heating the recording material in a nip portion formed by the pressure roller and the fixing roller. Fixing means;
Conveyance that conveys the recording material by switching the conveyance direction of the recording material in the fixing unit to either the forward direction or the reverse direction, with the conveyance direction of the recording material when image formation is normally performed as the forward direction. Means,
A jam detecting means for detecting the occurrence of jam in the recording material;
Control means for controlling the conveying means to convey a recording material in a reverse direction by a predetermined amount when occurrence of a jam is detected by the jam detecting means;
An image forming apparatus.

  According to the present invention, it is possible to facilitate a jam processing operation by a user in an image forming apparatus in which the leading edge of a recording material can be wound around the fixing roller one or more times when occurrence of a jam is detected. become.

Overall configuration of image forming apparatus Block diagram for explaining the system configuration of the image forming apparatus Diagram for explaining the jam detection method The figure for demonstrating Example 1. FIG. Flowchart for explaining the first embodiment The figure for demonstrating Example 2. FIG. Flowchart for explaining the second embodiment

Examples of the present invention will be described in detail below.
Example 1
In the first exemplary embodiment, there is a case where the leading edge of the paper may be wound around the fixing roller one or more times when the occurrence of the jam is detected based on the detection result by the paper discharge sensor disposed downstream of the fixing device. Forming device. The image forming apparatus according to the present exemplary embodiment separates the pressure roller and the fixing roller when the occurrence of the jam of the recording material is detected, and stops conveying the recording material after conveying the recording material by a predetermined amount in the reverse direction. The fixing roller is reversed. The predetermined amount is an amount until at least the recording material is wound less than one turn when the generated jam is wound around the fixing roller of the recording material. When the recording material is stopped after the predetermined amount of recording material is conveyed in the reverse direction, the recording material is wound around the fixing roller more than once around the recording material even when the generated jam is wrapped around the recording material. It will be resolved. For example, when the fixing roller is reversed by an amount corresponding to the difference between the distance from the fixing device to the paper discharge sensor and the circumference of the fixing roller for one turn, the sheet is wound around the fixing roller for more than one turn. If so, the condition is resolved. As a result, even when a jam occurs around the fixing roller, the toner fused portion of the paper wound around the fixing roller is prevented from overlapping with other portions of the paper, and the user pulls out the paper during the jam processing operation. The power required for is reduced.

  In this embodiment, it is assumed that image formation is performed in the order of yellow → magenta → cyan → black. Hereinafter, the same constituent elements provided for each color are represented by adding the suffixes indicating the respective colors to the same reference numerals. The subscripts for each color are Y for yellow, M for magenta, C for cyan, and B for black.

With reference to FIG. 1, an outline of the overall configuration of a laser printer as an image forming apparatus in this embodiment will be described.
In the image forming apparatus shown in FIG. 1, the color toner image developed by the rotatable image forming unit 100 loaded with four developing devices 20Y, 20M, 20C, and 20B is transferred onto the intermediate transfer member 9 in a multiple transfer manner. By further transferring the color toner image transferred to the intermediate transfer body 9 onto the paper 2 fed from the paper supply unit 101, a color toner image is formed on the paper 2. The image forming apparatus conveys the paper 2 to the fixing device 25 to fix the color toner image on the paper 2 and discharges the color toner image onto the paper discharge tray 37 on the upper surface of the apparatus main body by the paper discharge roller 36. The rotatable developing devices 20Y, 20M, 20C, and 20B are configured to be individually detachable from the image forming apparatus main body.

  The exposure to the image forming unit 100 is sent from a scanner unit 30 as an exposure unit (image forming unit). That is, when an image signal is applied to the laser diode, the laser diode irradiates the polygon mirror 31 with laser light modulated based on the image signal. The polygon mirror 31 is rotated at a high speed by a scanner motor 31a, and the surface of the photosensitive drum 15 (image carrier) on which the laser beam reflected by the polygon mirror 31 rotates at a constant speed via the imaging lens 32 and the reflection mirror 33. Are selectively exposed.

The configuration of the image forming unit 100 will be described in detail below.
The drum unit 13 is configured integrally with a photosensitive drum 15 that is a drum-type electrophotographic photosensitive member as an image carrier and a container 14 of a cleaning device that also serves as a holder for the photosensitive drum 15. The drum unit 13 is detachably supported with respect to the image forming apparatus main body, and is configured so that the unit can be easily replaced according to the life of the photosensitive drum 15. In the vicinity of the photosensitive drum 15, a cleaner blade 16 and a primary charging unit 17 are disposed. By transmitting the driving force of a driving roller (not shown) to one end of the photosensitive drum 15 in the rotation axis direction, the photosensitive drum 15 rotates in the direction of the arrow according to the image forming operation.

  The primary charging unit 17 is a charging unit using a contact charging system, and includes a conductive roller that comes into contact with the photosensitive drum 15. A voltage is applied to the conductive roller to uniformly charge the surface of the photosensitive drum 15. By irradiating the uniformly charged photosensitive drum 15 with laser light from the scanner unit 30, an electrostatic latent image is formed on the photosensitive drum 15.

  The cleaning device has a cleaner blade 16 that scrapes off the toner remaining on the photosensitive drum 15 after the toner attached to the electrostatic latent image on the photosensitive drum 15 is transferred to the intermediate transfer member 9 by the developing unit 102. The toner (waste toner) scraped off by the cleaner blade 16 is stored in the cleaning container 14. The waste toner stored in the cleaning container 14 is configured so that the cleaning container 14 is not filled earlier than the life of the photosensitive drum 15. Therefore, it is not necessary to perform an operation for emptying the cleaning container 14 other than the operation of replacing the drum unit 13 due to the life of the photosensitive drum 15.

  The developing unit 102 includes developing devices 20Y, 20M, 20C, and 20B that visualize the latent image formed on the photosensitive drum 15 by developing each color of yellow, magenta, cyan, and black. Each color developing device is detachably held by a developing rotary 23 that rotates about a shaft 22. During development, each developing device is rotated around the shaft 22 while being held by the developing rotary 23, and the developing device for performing development stops at a position facing the photosensitive drum 15. Further, after the developing sleeve is positioned so as to face the photosensitive drum 15 with a minute gap, a visible image is formed on the photosensitive drum 15. During color development, every time the intermediate transfer member 9 rotates, the development rotary 23 rotates 1/4 times so that the development unit of the color next to the development unit of the color previously developed comes to a position facing the photosensitive drum 15. To do. Development is performed in the order of the yellow developing unit 20Y, the magenta developing unit 20M, the cyan developing unit 20C, and the black developing unit 20B, and the intermediate transfer member 9 rotates four times to sequentially form yellow, magenta, cyan, and black toner images. The As a result, a full color toner image is formed on the intermediate transfer member 9.

FIG. 1 shows a state in which the yellow developing device 20Y is positioned and stationary at a position corresponding to the drum unit 13. The yellow developing device 20Y feeds the toner in the toner container to the application roller 20YR by a feeding mechanism. The application roller 20YR rotates counterclockwise in FIG. 1, and the developing sleeve 20YS rotates clockwise in FIG. Development sleeve 20YS
A thin layer of toner is applied to the outer periphery of the developing sleeve 20YS by the blade 20YB pressed against the outer periphery of the developing sleeve 20YB, and a charge is imparted to the toner by frictional charging. By applying a developing bias to the developing sleeve 20YS facing the photosensitive drum 15 on which the latent image is formed, toner development is performed by moving the toner from the developing sleeve 20YS to the position of the latent image on the photosensitive drum 15. In the magenta developing device 20M, the cyan developing device 20C, and the black developing device 20B, toner development is performed by the same mechanism as described above. The developing sleeves 20YS, 20MS, 20CS, and 20BS of the developing devices 20Y, 20M, 20C, and 20B are moved to the developing positions facing the photosensitive drum 15 when the developing devices are rotated and moved. Is connected to a driving circuit of a high-voltage power supply for development provided in. That is, each color developing device is selectively applied with a voltage at the time of developing each color and connected to a driving circuit.

  The intermediate transfer member 9 is a rotating endless belt and rotates in the direction of the arrow. The intermediate transfer member 9 receives four times of multiple transfers from the photosensitive drum 15 during the color image forming operation. The intermediate transfer member 9 that has received the transfer from the photosensitive drum 15 sandwiches and conveys the sheet 2 by a transfer roller (transfer mechanism) 10 to which a voltage is applied and the driving roller 5, thereby transferring each color toner on the intermediate transfer member 9 to the sheet 2. Transfer the image all at once. A non-image area on the outer periphery of the intermediate transfer member 9 is provided with a home position mark 9b for measuring the peripheral length of the intermediate transfer member 9 and as a reference for the image start timing of each color. Further, the image forming apparatus is provided with an optical sensor 9a for detecting the home position mark 9b of the intermediate transfer member 9.

  The paper feeding unit 101 feeds the paper 2 to the transfer unit 103. The paper feed unit 101 includes a cassette 1 that can store a plurality of sheets 2, a paper feed roller 3, and a registration roller 8. At the time of image formation, the paper feed roller 3 is rotationally driven according to the image forming operation, and the paper 2 in the cassette 1 is taken out one by one and conveyed to the registration roller 8. The registration roller 8 is provided with a shutter 11, and skew correction of the sheet 2 conveyed to the registration roller 8 is performed. Further, a tip detection sensor 6 for detecting that the paper 2 has reached the shutter 11 is provided. The registration roller 8 performs a non-rotating operation for causing the sheet 2 to stand still during the image forming operation and a rotating operation for conveying the sheet 2 toward the transfer unit 103. The non-rotating operation and the rotating operation of the registration roller 8 are performed based on the image formation timing and the timing at which the leading edge detection sensor 6 detects the paper 2, and thereby the position of the image and the paper 2 in the transfer process which is the next process. Matching is done. The registration roller 8 is disposed on the upstream side of the transfer unit 103 in the recording material conveyance direction when the recording material conveyance direction is the forward direction.

  The transfer unit 103 includes a swingable transfer roller 10. The transfer roller 10 as the contact means (transfer member) is movable in the diagonally up and down direction in FIG. 1 so as to contact or separate from the intermediate transfer body 9. That is, a position changing mechanism that switches between a state where the transfer roller 10 is in contact with the intermediate transfer body 9 or a position where the sheet 2 is sandwiched and a state where the transfer roller 10 is positioned away from the intermediate transfer body 9. Is provided. The position changing mechanism is driven by the driving unit 272, and the two states are switched by the driving force of the driving unit 272. While the image forming unit 100 forms toner images of four colors on the intermediate transfer member 9, that is, while the intermediate transfer member 9 rotates four times, the image formed on the intermediate transfer member 9 is not disturbed. The transfer roller 10 is positioned below the solid line and is separated from the intermediate transfer member 9.

  After the image forming unit 100 finishes forming the four color toner images on the intermediate transfer body 9, the transfer roller 10 is moved to a cam member (not shown) at a position indicated by a broken line in accordance with the timing of transferring the color image onto the paper 2. ) To the intermediate transfer member 9 through the paper 2 with a predetermined pressure. At the same time, a bias is applied to the transfer roller 10 and the toner image on the intermediate transfer body 9 is transferred to the paper 2. Here, since the intermediate transfer body 9 and the transfer roller 10 are respectively driven to rotate, the sheet 2 sandwiched between the two is subjected to a transfer process and is conveyed in the upper left direction in FIG. Is conveyed toward the fixing device 25 where the image forming operation is performed.

  The fixing device 25 applies heat and pressure to the unfixed toner image on the recording material to fix it on the recording material. The fixing device 25 includes a fixing roller 26 and a pressure roller 27. The pressure roller 27 contacts the fixing roller 26 with a predetermined pressure, and a fixing nip portion N having a predetermined width is formed at a contact portion between the pressure roller 27 and the fixing roller 26. In a state where the fixing nip portion N is heated to a predetermined temperature and adjusted in temperature, the paper 2 transferred from the transfer portion 103 and onto which the unfixed toner image is transferred is nipped and conveyed in the fixing nip portion N. Specifically, an image surface on which an unfixed toner image of the paper 2 is formed is introduced to the fixing nip portion N between the fixing roller 26 and the pressure roller 27 so as to face the fixing roller 26, and the fixing nip portion At N, the sheet 2 is nipped and conveyed while the image surface is in close contact with the outer surface of the fixing roller 26. In the process in which the sheet 2 is nipped and conveyed through the fixing nip N, the sheet 2 is heated by the fixing roller 26 and the unfixed toner image on the sheet 2 is heated and fixed. The position of the pressure roller 27 is the first position where the fixing roller 26 and the pressure roller 27 form a nip portion, and the position where the fixing roller 26 and the pressure roller 27 separate from each other without forming the nip portion. And a position changing mechanism for switching to any one of the positions. The first position and the second position are switched by the driving force of the driving unit 271 that drives the position changing mechanism.

  Next, an operation when image formation is performed by the image forming apparatus configured as described above will be described. First, the sheet feeding roller 3 shown in FIG. 1 is rotated to separate one sheet 2 in the cassette 1 and conveyed to the registration roller 8. On the other hand, the photosensitive drum 15 and the intermediate transfer member 9 rotate in the direction of the arrow shown in the figure, the surface of the photosensitive drum 15 is uniformly charged by the primary charging unit 17, and light irradiation based on the yellow image signal is performed by the scanner unit 30. A yellow image latent image is formed on the drum 15. When the latent image is formed, the yellow developing device 20Y is driven, and a voltage having the same polarity as the charged polarity of the photosensitive drum 15 is applied so that yellow toner adheres to the latent image of the yellow image on the photosensitive drum 15. Perform yellow development. A voltage having a characteristic opposite to that of the toner is applied to the intermediate transfer member 9 from a power source to primarily transfer the yellow toner on the photosensitive drum 15 onto the intermediate transfer member 9.

  When the primary transfer of the yellow toner to the intermediate transfer member 9 is completed as described above, the developing rotary 23 rotates and the next magenta developing device 20M is moved to the position facing the photosensitive drum 15, and is positioned in the same manner as the yellow image. Thus, the latent image of the magenta image is developed. Subsequently, cyan and black latent images are formed and developed, and toner transfer onto the intermediate transfer member 9 is sequentially performed to form a color image composed of toners of four colors of yellow, magenta, cyan, and black on the surface of the intermediate transfer member 9. . Then, after a color image is formed on the surface of the intermediate transfer member 9, the paper 2 that has been waiting by the registration roller 8 is conveyed, and the transfer roller 10 presses the paper 2 against the intermediate transfer member 9, and the transfer roller 10. A bias having a reverse characteristic to that of toner is applied. As a result, the color toner image on the intermediate transfer body 9 is transferred to the paper 2. After the transfer of the toner image from the intermediate transfer member 9 to the paper 2 is completed, the transfer roller 10 is separated from the intermediate transfer member 9.

  While the sheet 2 is nipped and conveyed between the transfer roller 10 and the intermediate transfer member 9 to transfer the toner image, the latent image of the yellow image of the next image (second page) is transferred to the photosensitive drum 15. Formed. After the yellow image latent image is formed on the photosensitive drum 15 and before the next magenta image latent image starts to be formed, the transfer roller 10 is separated from the contact position where the sheet 2 is pressed against the intermediate transfer body 9. Move to position. The sheet 2 is peeled off from the intermediate transfer member 9 and conveyed to the fixing device 25, where toner fixing is performed. After the toner is fixed, the sheet 2 is discharged onto the discharge tray 37 at the top of the main body via the discharge roller pair 36, and the image forming operation is completed. After the toner image is transferred from the intermediate transfer member 9 to the sheet 2, the charging roller 39 (hereinafter referred to as “ICL roller”) comes into contact with the intermediate transfer member 9, so that residual toner remaining on the intermediate transfer member 9 is removed from the toner. Is charged to a polarity opposite to the normal charging polarity.

After charging the residual toner, the ICL roller 39 is separated from the intermediate transfer member 9. During continuous image formation, a yellow image latent image of the next image is formed on the photosensitive drum while the ICL roller 39 is in contact with the intermediate transfer member 9. When the yellow image transferred onto the intermediate transfer member 9 passes through the contact position by the ICL roller 39, the ICL roller 39 is separated from the intermediate transfer member 9. The residual toner charged by the ICL roller 39 is electrostatically reversely transferred to the photosensitive drum 15 at the primary transfer position, and is collected in the cleaning container 14 by the cleaner blade 16. By simultaneously performing the reverse transfer process of the residual toner and the transfer process of transferring the yellow image of the next image from the photosensitive drum 15 to the intermediate transfer body 9, the throughput of image formation can be improved. it can.

  FIG. 2 is a block diagram for explaining the system configuration of the image forming apparatus.

  The image forming apparatus system according to the present exemplary embodiment includes a host computer 200, an engine control unit 202 of the image forming apparatus, a controller 201 that controls the engine control unit 202, and a video interface unit 210 that connects the controller 201 and the engine control unit 202. . The video interface unit 210 includes a serial communication unit and an image forming signal unit. The serial communication unit transmits a command from the controller 201 to the engine control unit 202 and returns a status from the engine control unit 202 to the controller 201. The image forming signal unit communicates image data between the controller 201 and the engine control unit 202. The engine control unit 202 has a CPU 211. The CPU 211 controls operations of the image generation unit 212, the fixing control unit 213, the high voltage control unit 214, the paper feed control unit 215, the driving unit 216, and the sensor control unit 217, respectively.

  The image generation unit 212 generates a / TOP signal 220 that is a vertical synchronization signal for image formation, and performs control related to image formation such as scanner motor control and laser output control. The fixing controller 213 controls the heating device for the fixing roller 26. The high voltage control unit 214 performs voltage control of the primary charging unit 17 and the like. The paper feed control unit 215 performs drive control of the paper feed roller 3 and the registration roller 8. The drive unit 216 controls the drive roller 5, the photosensitive drum 15, a motor that drives the developing rotary 23, a motor 261 that drives the fixing roller 26, a motor 81 that drives the registration roller 8, and the like. The drive unit 216 controls a drive unit 271 that operates a position change mechanism that changes the position of the pressure roller 27, a drive unit 272 that operates a position change mechanism that changes the position of the transfer roller 10, and the like. The sensor control unit 217 performs acquisition control of detection values of various sensors such as the leading edge detection sensor 6, the paper discharge sensor 38, and the optical sensor 9 a for detecting that the paper 2 has reached the registration roller 8.

FIG. 3 is a diagram for explaining a method for detecting a jam of the paper 2 in the fixing device.
The paper discharge sensor 38 is provided at a position downstream of the conveyance direction when the conveyance direction is forward with respect to the fixing nip portion N, and a recording material detection unit that detects that the paper 2 discharged from the fixing device 25 has passed. It is. The image forming apparatus determines that a jam has occurred when the leading edge of the paper 2 has not passed the paper discharge sensor 38 within a predetermined time L / V from the time when the leading edge of the paper 2 reaches the fixing nip N. To do. Here, L is the distance along the conveyance path of the sheet 2 from the fixing nip portion N to the sheet discharge sensor 38, and V is the conveyance of the sheet 2 discharged from the fixing device 25 when normal image formation is performed. Speed.

That is, when a determination result regarding whether or not a jam has occurred is generated, a predetermined time has already passed since the leading edge of the sheet 2 reaches the fixing nip N. Therefore, when the distance from the fixing nip portion N to the paper discharge sensor 38 is long and the predetermined time is long, and when it is detected that a jam has occurred, the paper 2 has already been wound around the fixing roller 26 for one or more times. There can be. In order to detect the occurrence of jam at a timing before the leading edge of the paper 2 is wound around the fixing roller 26 for one or more times when a jam occurs, the diameter R of the fixing roller 26 is

L <πR (1)

Therefore, it is necessary to shorten the distance from the fixing nip portion N to the paper discharge sensor 38. On the other hand, since the vicinity of the fixing nip portion N becomes high temperature due to the heat of the fixing roller 26, the fixing nip portion N and the paper discharge sensor 38 should not be too close for the normal operation of the paper discharge sensor 38. It is also necessary to.

  Here, in the image forming apparatus according to the present exemplary embodiment, when the discharge roller 38 is arranged so that the diameter of the fixing roller is small and Equation 1 is satisfied, the discharge sensor 38 and the fixing nip portion N are too close to each other. It is assumed that this is a configuration. In other words, if the paper discharge sensor 38 has to be disposed at a position where L> πR is satisfied, and the jam occurs, the jam is generated before the leading edge of the paper 2 is wound around the fixing roller 26 for one or more rounds. It is assumed that the paper discharge sensor 38 cannot be disposed at a detectable position. Accordingly, when the occurrence of a jam is detected by the paper discharge sensor 38, the leading edge of the paper 2 may be wound around the fixing roller 26 for one or more turns, and the paper 2 may overlap with the fixing roller 26. In this case, the toner may be fused at the portion where the sheets 2 overlap each other. If it does so, there exists a problem that the operation | work which the user pulls out the paper 2 in order to eliminate jam becomes difficult.

  Therefore, in the image forming apparatus of this embodiment, when the occurrence of a jam is detected based on the detection result by the paper discharge sensor 38, the fixing roller 26 is reversely rotated for a predetermined time. As a result, when the sheet 2 is wound around the fixing roller 26 due to a jam, the state where the leading edge of the sheet 2 is wound around the fixing roller 26 one or more times is resolved, and the toner is removed at the portion where the sheets 2 overlap each other. Is prevented from being fused. In the present exemplary embodiment, the fixing roller 26 conveys the sheet while switching the conveyance direction between the forward direction and the opposite direction when the image formation is normally performed. The fixing roller 26 is rotated by a motor 261 whose rotation direction is switched between forward rotation and reverse rotation. When the motor 261 rotates the fixing roller 26 forward, the paper transport direction is switched to the forward direction, and when the motor 261 reverses the fixing roller 26, the paper transport direction is switched to the reverse direction.

  FIG. 4 is a diagram for explaining a method of avoiding toner fusion by eliminating the overlap of the overlapping portions 2a of the paper 2 that has been wound around the fixing roller 26 for one or more turns when a jam is detected.

  In the image forming apparatus of this embodiment, when it is detected that a jam as shown in FIG. 4A has occurred, the pressure roller 27 is separated from the fixing roller 26 as shown in FIG. 4B. Then, the transfer roller 10 is separated from the intermediate transfer member 9. Further, the sheets 2 overlap each other by rotating the fixing roller 26 reversely (rotating counterclockwise in the figure) until the state where the leading end of the downstream side of the sheet 2 is wound around the fixing roller 26 is resolved. The toner is prevented from fusing at the part. The time for reversing the fixing roller 26 and transporting the paper in the reverse direction is at least the time {(t1-t2) −πR / V} calculated by the following equation. Here, t1 is the time when the jam is detected, and t2 is the time when the leading edge of the sheet 2 passes through the fixing nip portion N. It can be said that the time for reversing the fixing roller 26 by rewriting this equation is at least (L−πR) / V or more.

  As described above, “the configuration in which the paper discharge sensor 38 cannot be disposed at a position where the occurrence of the jam can be detected before the leading edge of the paper 2 is wound around the fixing roller 26 for one or more rounds when the jam occurs”. It can also be said that L> πR holds.

The engine control unit 202 is connected to the controller 20 via the video interface unit 210.
When a print start command is received from 1, the sheet 2 on which the toner image is placed is conveyed to the fixing device 25 by the image forming operation described above. FIG. 5 is a flowchart showing processing for detecting occurrence of a jam in the fixing device 25 of the paper 2 on which the toner image is formed. When the leading edge of the sheet 2 reaches the fixing nip N (step 510), the CPU 211 starts a jam detection timer (step 511). The CPU 211 determines whether or not the paper discharge sensor 38 has reacted within a predetermined time (= distance from the fixing nip portion N to the paper discharge sensor 38 / conveying speed) after starting the jam detection timer (step) 512). When the paper discharge sensor 38 reacts within the predetermined time (when the paper 2 passes through the paper discharge sensor 38 within the predetermined time) (step 512: Yes), the CPU 211 has jammed the paper 2 in the fixing device 25. It is determined that there is not, and the processing of this flowchart is temporarily ended. Each time a new sheet 2 is supplied from the transfer unit 103 to the fixing device 25, the process of this flowchart is executed. If the paper discharge sensor 38 does not react within the predetermined time (step 512: No), the CPU 211 determines that a jam has occurred (step 513).

  When the occurrence of the jam is detected, the CPU 211 calculates a time for rotating the fixing roller 26 in the reverse direction (step 514). Here, the time for reversing the fixing roller 26 is calculated as a time that can be eliminated by assuming that a jam occurs in which the sheet 2 is wound around the fixing roller 26 for one or more turns. To do. Specifically, the CPU 211 calculates the reverse rotation time of the fixing roller 26 from ((t1−t2) −πR / V).

  Next, the CPU 211 separates the pressure roller 27 from the fixing roller 26 and also separates the transfer roller 10 from the intermediate transfer body 9 (step 515). Further, the CPU 211 stops the fixing roller 26 (step 516) and further reverses the fixing roller 26 (step 517). The CPU 211 calculates the time for which the fixing roller 26 is reversely rotated by the above formula (2) or formula (3).

  Next, the CPU 211 checks whether or not the reverse rotation time of the fixing roller 26 has exceeded the calculated time (step 518). Here, the CPU 211 starts a timer at the timing when the reverse rotation of the fixing roller 26 is started, and determines whether the count time of the timer is equal to or longer than the calculated time. If the reverse rotation time of the fixing roller 26 has exceeded the calculated time (step 518: Yes), the CPU 211 stops the fixing roller 26 (step 519) and ends the process. If the reverse rotation time of the fixing roller 26 has not exceeded the calculated time (step 518: No), the CPU 211 continues the reverse rotation operation of the fixing roller 26.

Here, the image forming apparatus according to the present exemplary embodiment is configured such that the user can manually remove or move a part of the exterior part of the apparatus main body to access the recording material conveyance path. For example, in this embodiment, by moving the exterior component 40 shown in FIG. 1 so as to be tilted to the left in FIG. 1, it is possible to access the conveyance path downstream from the transfer unit 103 and upstream from the fixing device 25. . The user can perform the jam processing by moving the exterior component 40 and pulling out the recording material from the conveyance path. The configuration for enabling the jam processing by the user is not limited to this example, but the configuration is such that the user can perform the jam processing work at a position some distance from the fixing device 25 in a high temperature state. Is desirable. In the image forming apparatus according to the present exemplary embodiment, when the recording material is wound around the fixing roller 26 when a jam occurs, the recording material is not wound around the fixing roller 26 due to the reverse rotation of the fixing roller 26. become. In this state, even if the leading edge of the recording material protrudes downstream from the fixing device 25 in the forward conveyance direction, only the length of about one turn of the fixing roller 26 protrudes. For this reason, a configuration in which the user pulls out the recording material from the downstream side of the fixing device 25 is not preferable because it is necessary to bring a hand close to the fixing device 25 in a high temperature state. Therefore, in the example of FIG. 1, the user pulls out the recording material from the upstream side of the fixing device 25. However, for example, an image forming apparatus having a configuration in which an operation unit that allows the user to manually rotate the roller for conveyance is provided and the user can manually convey the recording material along the conveyance path. Then, a configuration in which the recording material is pulled out from the downstream side of the fixing device 25 is also possible. In that case, the user can manually convey the recording material until the leading end of the recording material is sufficiently away from the fixing device 25, access the conveyance path on the downstream side of the fixing device 25, and pull out the recording material. .

  According to the present embodiment, when a jam occurs, even if the sheet is wound around the fixing roller for one or more turns, the state can be solved. Therefore, when the occurrence of a jam is detected, the toner can be prevented from fusing at the portion where the paper overlaps on the fixing roller, so that it is possible to reduce the force required for the user to pull out the paper for jam processing. It becomes.

(Example 2)
In the first embodiment, when the occurrence of a jam is detected, the pressure roller is separated from the fixing roller, the transfer roller is separated from the intermediate transfer member, and the fixing roller is rotated in the reverse direction so that the sheet is wound around the fixing roller one or more times. An example of canceling the state has been described.
In the second embodiment, when the occurrence of a jam is detected, the pressure roller is separated from the fixing roller, the transfer roller is separated from the intermediate transfer member, and the registration roller is reversed, so that the sheet is wound around the fixing roller by one or more times. An example of canceling the state will be described.

FIG. 6 is a diagram for explaining a method for eliminating a state in which the sheet 2 is wound around the fixing roller 26 one or more times when the occurrence of a jam is detected.
Also in the image forming apparatus of the present embodiment, the paper discharge sensor 38 is disposed at a position where the occurrence of the jam can be detected before the leading edge of the paper 2 is wound around the fixing roller more than once when the jam occurs. It is assumed that the configuration is not possible. For this reason, when the occurrence of a jam is detected by the paper discharge sensor 38, the paper 2 may already be wound around the fixing roller 26 for one or more turns as shown in FIG. At this time, as shown in FIG. 6B, the image forming apparatus separates the pressure roller 27 from the fixing roller 26 and also separates the transfer roller 10 from the intermediate transfer member 9. Further, when the sheet 2 is wound around the fixing roller 26 for one or more turns, the registration roller 8 is reversed so that the state can be eliminated.

  The time for reversing the registration roller 8 is calculated by Formula 2 or Formula 3 as in the first embodiment. In this embodiment, the registration roller 8 conveys the sheet while switching the conveyance direction between the forward direction and the reverse direction when the image formation is normally performed. The registration roller 8 is rotated by a motor 81 whose rotation direction is switched between forward rotation and reverse rotation. When the motor 81 rotates the registration roller 8 forward, the paper conveyance direction is switched to the forward direction, and when the motor 81 reverses the registration roller 8, the paper conveyance direction is switched to the reverse direction.

FIG. 7 is a flowchart for explaining the present embodiment.
When the engine control unit 202 receives a print start command from the controller 201 via the video interface unit 210, the engine control unit 202 conveys the sheet 2 on which the toner image is placed to the fixing device 25 by the image forming operation described above. When the leading edge of the sheet 2 reaches the fixing nip N (710), the CPU 211 starts a jam detection timer (711). When the paper discharge sensor 38 has not reacted within a predetermined time (= distance from the fixing nip portion N to the paper discharge sensor 38 / conveyance speed) after starting the jam detection timer (712), the CPU 211 It is determined that a jam has occurred (713).

If the CPU 211 determines that a jam has occurred, the CPU 211 reverses the registration roller in order to eliminate the state in which the sheet 2 is wound around the fixing roller 26 for one or more times (= (t1-t2) −
(πR / V) is calculated (714).

  Next, the CPU 211 moves the pressure roller 27 away from the fixing roller 26 and moves the transfer roller 10 away from the intermediate transfer member 9 (715). Further, the CPU 211 stops the fixing roller 26 (716), and further reverses the registration roller 8 (717). The CPU 211 calculates the time for reversing the registration roller 8 using the above formula (2) or formula (3).

  Next, the CPU 211 confirms whether or not the reverse rotation time of the registration roller 8 has exceeded the calculated time (518). Here, the CPU 211 starts a timer at the timing when the reverse rotation of the registration roller 8 is started, and determines whether or not the count time of the timer is equal to or longer than the calculated time. If the reverse rotation time of the registration roller 8 has exceeded the calculated time, the CPU 211 stops the registration roller 8 (719) and ends the processing. If the reverse rotation time of the registration roller 8 has not exceeded the calculated time, the CPU 211 continues the reverse rotation operation of the registration roller 8.

  According to the present exemplary embodiment, when a jam occurs, the image forming apparatus that cannot detect the occurrence of the jam before the leading edge of the sheet is wound around the fixing roller for one or more turns, and then the fixing is performed after the occurrence of the jam is detected. The state in which the sheet is wound around the roller more than once is eliminated. Therefore, when the occurrence of a jam is detected, the toner can be prevented from fusing at the portion where the paper overlaps on the fixing roller, so that it is possible to reduce the force required for the user to pull out the paper for jam processing. It becomes.

  The above-described embodiments can be variously modified based on the gist of the present invention, and the scope of the present invention is not limited to the above-described embodiments. For example, in each of the above embodiments, an example in which the present invention is applied to an image forming apparatus having a rotary developing device has been described. However, the present invention can also be applied to an image forming device in which a plurality of color developing devices are arranged in parallel. . In addition, the example of the image forming apparatus configured to transfer the toner image transferred from the photosensitive drum to the intermediate transfer member onto the sheet has been described, but the image forming apparatus configured to transfer the toner image directly from the photosensitive drum to the sheet is also described. The present invention is applicable. When detecting a jam, at least one of an operation of separating the fixing roller and the pressure roller, an operation of rotating the fixing roller, an operation of rotating the registration roller, and an operation of separating the transfer roller 10 and the driving roller 5 may be performed. Any combination may be performed.

26: fixing roller 261: drive motor 27: pressure roller 25: fixing device 38: paper discharge sensor 211: CPU

Claims (8)

A fixing unit having a pressure roller and a fixing roller, and fixing the unfixed toner image on the recording material by sandwiching and heating the recording material in a nip formed by the pressure roller and the fixing roller;
Conveyance that conveys the recording material by switching the conveyance direction of the recording material in the fixing unit to either the forward direction or the reverse direction, with the conveyance direction of the recording material when image formation is normally performed as the forward direction. Means,
A jam detecting means for detecting the occurrence of jam in the recording material;
Control means for controlling the conveying means to stop the conveyance of the recording material after conveying the recording material by a predetermined amount in the reverse direction when the occurrence of a jam is detected by the jam detecting means;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the predetermined amount is an amount until at least the recording material is wound less than one turn when the generated jam is a winding of the recording material around the fixing roller. The position of the pressure roller includes a first position where the fixing roller and the pressure roller form a nip portion, and a second position where the fixing roller and the pressure roller separate from each other without forming a nip portion. With a position change mechanism to switch to either
3. The image according to claim 1, wherein the control unit controls the position changing mechanism so that the position of the pressure roller becomes the second position when occurrence of a jam is detected by the jam detection unit. Forming equipment. The conveying means includes a driving means for rotating the fixing roller by switching the rotation direction to either normal rotation or reverse rotation, and switching the conveyance direction of the recording material to the forward direction by rotating the fixing roller forward. To reverse the recording material conveyance direction,
The image forming apparatus according to claim 1, wherein the control unit controls the driving unit to reversely rotate the fixing roller when the occurrence of a jam is detected by the jam detection unit. A registration roller disposed on the upstream side of the recording material conveyance direction when the recording material conveyance direction is forward with respect to the transfer means for transferring the toner image to the recording material,
The conveying means includes a driving means for rotating the registration roller by switching the rotation direction to either normal rotation or reverse rotation, and switching the conveyance direction of the recording material to the forward direction by rotating the registration roller forward. To reverse the recording material conveyance direction,
The image forming apparatus according to claim 1, wherein the control unit controls the driving unit to reversely rotate the registration roller when the occurrence of a jam is detected by the jam detection unit. The jam detection means is disposed downstream of the nip portion in the recording material conveyance direction when the recording material conveyance direction is the forward direction, and detects the recording material discharged from the fixing means. Based on the detection result by, detect the occurrence of jam,
The control means, when the occurrence of a jam is detected by the jam detection means, at least a distance along the recording material conveyance path from the nip portion to a position where the recording material detection means detects the recording material 6. The conveying unit according to claim 1, wherein the conveying unit is controlled so that the recording material is conveyed in a reverse direction by a length obtained by subtracting a circumferential length of the fixing roller from one circumference. Image forming apparatus. The recording material detection means is L> πR, where L is a distance along the recording material conveyance path from the nip portion to a position where the recording material detection means detects the recording material, and R is a diameter of the fixing roller. Is placed at a position where
The jam detecting means has a conveyance speed of the recording material discharged from the fixing means when image formation is normally performed as V, and a leading end downstream in the conveyance direction of the recording material when the conveyance direction is the forward direction. The image forming apparatus according to claim 6, wherein the occurrence of a jam is detected when the recording material detection unit does not detect the passage of the recording material within a time L / V after reaching the nip portion.   The image forming apparatus according to claim 7, wherein when the occurrence of a jam is detected by the jam detection unit, the control unit sets the time for conveying the recording material in the reverse direction to at least (L−πR) / V or more. apparatus.

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